**3. Effects of statins in animal studies literature review**

A total of 60 articles were found. When duplicates and those that did not meet the criteria were excluded, there were 15 publications left that were included in the research.

**Table 1** shows the results of this review. A total of 15 papers were included in the analysis. In seven studies, statins were shown to increase the formation of new bone. In two studies, statins promoted better osseointegration of dental implants and in one, there were no significant differences. In five studies, use of statins led to improved contact between the bones and the surface of the implant, and in three

*Use of Statins in Dental Implantology and Their Impact on Osseointegration: Animal Studies DOI: http://dx.doi.org/10.5772/intechopen.108953*

*Use of Statins in Dental Implantology and Their Impact on Osseointegration: Animal Studies DOI: http://dx.doi.org/10.5772/intechopen.108953*

#### **Table 1.**

*A total of 15 papers that were included in the analysis with their number of test subjects, number of implants that were placed in the study, place where implant was inserted, surface of implant and dosage used in each animal research, and final conclusion of each study.*

studies, less mobility of the implant could be demonstrated. In two studies, there were no significant differences in contact between bone and implant, regardless of the statin use.

One study demonstrated more bone formation if simvastatin was administered topically than systemically orally. Tibolone also showed good results in osseointegration compared to simvastatin.

Kellesarian et al. [15] reviewed studies performed on 19 laboratory animals in which simvastatin was administered systemically and locally, specifically orally, subcutaneously, and intraosseously. Better osseointegration and better contact of the implant surface with the newly formed bone were demonstrated in the simvastatin group. A total of 13 studies were performed on female rats, 1 study was on male rats, and 5 studies were performed on dogs of indeterminate sex. Statins were used topically in 12 studies, statins were applied directly to bone cavities in five studies and they were applied systemically in two studies. The dose of systemically administered statins was between 0.25 and 50 mg/kg/day. In two studies, propylene glycol and fluvastatin were used at a dose of 3–300 μg and were applied to the bone bed of the implant before implant placement. Titanium implants were used in all studies.

Studies by Fang et al., Kwon et al., and Faraco-Schwed et al. [16–18] reported that the total number of implants placed in subjects ranged between 16 and 96 implants

per research. The total number of implants utilized was not reported in 14 studies. Implants were placed in the tibia and femur in 13 and in 4 studies, respectively. In a study by Kwon et al., 16 implants were placed in the tibia and femur [17]. Fang et al. in their research study work on 36 female rats divided into 3 groups. In the first group, the surface of implants implanted in the tibia is covered with a mixture of hydroxylapatite and simvastatin in the amount of SIM 10−7 M (M = 1 mol/liter), in the second group, the surface of implants is covered with the same combination only in the amount of 10−6 M, and in the third group, only hydroxylapatite is applied on the surface of implants. Histomorphometric analysis was performed after 2, 4, and 12 weeks and better contact of the newly formed bone with the implant surface was found as well as a higher volume of newly formed bone in the first two groups as opposed to the third group [16]. Kwon et al. performed the research on 3 male rabbits, divided into three groups. A total of 16 implants measuring 3.5 × 8 mm are placed in the tibia and femur. The first group is control and implants are placed without additional surface treatment. In the second group, implants surface is coated only with hydroxylapatite and in the third group, implants surface is covered with hydroxylapatite and simvastatin and a concentration of 535 μg.

Follow-up after 4 weeks was done by micro-CT analysis and biomechanical examination during which a significantly higher volume of newly formed bone and less implant mobility were observed in the third group [17]. Faraco-Schwed et al. conducted a study in which they topically administered statins to 16 male rabbits divided into 4 groups. They used 32 titanium implants implanted in the tibia measuring 3.25 × 8.5 mm. The first group received 0.25 mL of simvastatin gel (30 mg/mL) topically over 28 days, the second group over 56 days, while the third and fourth groups represented the control group. Biomechanical control after 4 and 8 weeks showed significantly less mobility in the second group compared to the fourth, while in the first and third groups there were no statistically significant differences [18].

Mansour et al. studied 10 dogs that received titanium implants in the mandible measuring 3.5 × 10 mm. The duration of the study was 18 months. The first group received simvastatin 150 mg topically *via* implant surface and the second group was the control. Histological analysis of the preparation after 4 and 12 weeks showed a significantly higher amount of newly formed bone in the first compared with the control group [19].

Nyan et al. used 24 male rats divided into 6 groups. The first group was the control. The second group used implants where the surface was treated only by the micro-oxidation technique, while the third group used implants where the surface was treated with micro-oxidation and coated with simvastatin (SIM) in the amount of SIM 25 μg and in the fourth group, the amount of simvastatin used to cover the surface of implants was 50 μg. Micro-CT analysis and histological analysis were performed after 2 and 4 weeks and the results showed significantly higher volume of newly formed bone, better contact of newly formed bone, and implant surface as well as a larger volume of mineralized newly formed bone. Titanium implants measuring 1.8 × 5.0 mm were implanted in the animals' tibia [20].

Pauly et al. divided 80 female rats into 4 groups. The first group was control, while the second group used implants where the surface was treated only with poly D, l-lactide acid (PDDLA) and the third and fourth groups used PDLLA + simvastatin 5.5 μg and PDLLA + simvastatin 90 μg per implant surface. Histological and biomechanical analysis after 8 weeks showed a significantly higher volume of newly formed bone as well as better contact between the surface of the implant and the newly formed bone and significantly less mobility of the implant in the third and fourth groups. Titanium implants measuring 1.4 × 5 mm implanted in the femur were used in the study [21].

#### *Use of Statins in Dental Implantology and Their Impact on Osseointegration: Animal Studies DOI: http://dx.doi.org/10.5772/intechopen.108953*

Yang et al. implanted 96 titanium implants in a total of 48 female rats with removed ovaries. The implants measured 2.2 × 4.0 mm. The first group underwent ovariectomy, while rats in the other two groups underwent ovariectomy and the surface of implants was coated with a concentration of simvastatin 10−7 M for the first group and in the second group with 10−6 M. Histomorphometric analysis after 1, 2, 4, and 12 weeks showed a significantly higher volume of newly formed bone and better contact of the implant surface with the newly formed bone in the first two groups [22].

Moriyama et al. conducted their two studies on a total of 186 female rats. The first study was conducted on 60 rats divided into 5 groups that received titanium implants measuring 1 × 1.5 mm in the tibia. Throughout all five groups, authors combined different amounts of propylene glycol alginate (PGA) and fluvastatin (FLU) at different concentrations topically across the implant surface. The first group was the control, while the second group received only PGA, the third group topically received PGA and FLU 3 μg on the surface of the implant, the fourth group received PGA + SIM 15 μg on the surface of implant, and the fifth group received PGA and FLU 75 μg on the surface of the implant. Histomorphometrically, group 5 showed a significantly higher volume of newly formed bone compared to other groups, while there was no significant difference in the quality of contact between the implant surface and the newly formed bone in all five groups. The second study was performed on 126 female rats divided into 6 groups, 21 subjects each. The first group subjects did not receive any topical statin administration and it formed the control group. The second group received topically only PGA, the third group received FLU in the amount of 3 μg; the fourth group received FLU 15 μg, the fifth group FLU 75 μg, and the sixth group received FLU in the amount of 300 μg on the surface of the implant. All animals had titanium implants measuring 1 × 1.5 mm in the tibia. After the first week, the volume of the newly formed bone was lower in group six compared to other groups and after the second week, the volume of newly formed bone and bone contact with the implant was higher in the fifth group compared to other groups [23, 29].

In their review paper, Moraschini et al. [30] also summarize and analyze similar studies as Kellesarian et al. The discussion explained the mechanism of action of statins on the process of osseointegration. Authors concluded that statins enhanced the action of bone-morphogenic protein-2 (BMP-2) which in turn acted on enhanced osteoblastic activity and the formation of new bone. Authors further claimed that in the above studies in which FLU was used in rats, no changes were observed in the form of an increase in the liver enzymes alanine aminotransferase (ALT) or aspartate aminotransferase (AST). The higher the dose used in the studies, the greater the volume of newly formed bone and better seal of newly formed bone and implant surface in the first 2 weeks, which was evident in the study by Moriyama et al.

Türer et al. divided 32 rats into 4 groups: group C-14 (control), group R-14, group C-28 (control), and group R-28. Each animal underwent a unilateral, standard vertical osteotomy on the right side of the mandible, extending from the tooth to the mandibular base. Sterile saline absorbent collagen sponge was applied to the fracture area in groups C-14 and C-28, while an absorbent collagen sponge with saline containing 1 mg rosuvastatin was applied to the fracture area in groups R-14 and R-28. Animals in groups C-14 and R-14 were euthanized on day 14 and the animals in groups C-28 and R-28 were euthanized on day 28 after surgery. Stereological analyses were performed. New areas of bone and connective tissue volume were measured. Stereological analysis showed that the R-14 group had significantly more new bone after 2 weeks compared to the C-14 group. The volume of connective tissue was also significantly higher in R-14. Differences in connective tissue volume and new bone

were not statistically significant upon comparison of groups C-28 and R-28. Topically applied rosuvastatin enhanced early bone regeneration in rats with mandibular fracture [31].

Keuroghlian et al. investigated mice with the assumption that hyperlipidemia negatively affected the osseointegration of dental implants because a high-fat diet had significant detrimental effects on bone density and volume. The authors placed a group of male mice on a high-fat diet and a control group on a regular diet. After 12 weeks, every animal received a titanium implant in the femur. Animals were humanely sacrificed 4 or 8 weeks after implantation, and the results showed that a high-fat diet significantly reduced bone density and strength and that osseointegration was poorer [32].

The work of Mahrous, who investigated the topical application of simvastatin in gel form for the treatment of peri-implant mucositis, was found in the Cochrane Central database. The author tested the proven anti-inflammatory effect of statins on the inflamed mucosa surrounding dental implants. The hypothesis was that 1.2% of simvastatin gel would reduce inflammation around the implant. The pilot study involved 44 subjects divided into a test and a control group. The test group received topically simvastatin gel that was applied with a blunt-tipped needle around the implant while the control group received a placebo. The inflammatory condition was determined at the beginning of the study, 24 hours later, after 1 week, and after 1 month by clinical indications for inflammation and biochemical markers of inflammation collected around the implant. The study included individuals of both sexes who had no signs of bone resorption around the implant by more than 1 mm as established by X-ray analysis. The results showed that the greatest reduction in inflammation occurred in the first 24 hours, but there were no statistically significant differences in the levels of cytokines IL-1β, IL-6, IL-8, and TNF-α between the test and control group as well as no significant differences in periodontal probing depth [24].

Ayukawa et al. performed the animal study on 10 female rats that were 30 weeks old. Ten titanium implants were placed in both tibias and measured 1 mm in diameter and 1.5 mm in length. Experimental group received intraperitoneally 10 mg/kg of simvastatin, and the control group received isotonic saline instead. Both groups showed that the newly formed bone was thought to be in direct contact with the implant surface. Despite direct contact of the new bone and implant surface, the experimental group showed occasional evidence of unmineralized connective tissue, including fibroblast-like cells and blood vessels, on implant surface [25].

Rongyao Xu et al. performed implants in oral cavity on 30 male rats that were postoperatively randomly divided into three groups. The first group received 25 mg/ kg of simvastatin orally, the second group received simvastatin injections in the amount 0.8 mg/0.05 mL around the implant every day, and the third group was the control. Simvastatin promoted osseointegration of the implant. Rats that were treated with simvastatin had more newly formed bone that had a woven appearance than control group rats as revealed by H&E staining. In addition to that, the volume of bone tissue was significantly higher in rats that received simvastatin locally in comparison with the group that received simvastatin orally [26].

Hoon Yun et al. researched the effect of ultraviolet (UV) and simvastatin (SIM) treatment on the osseointegration of dental titanium implants in rabbit tibias at two different time points. Implants were sandblasted, large-grit, and acid-etched (SLA) and surface alterations due to simvastatin treatment were analyzed with an infrared spectrometer. Implants were divided into four groups depending on the type of surface treatment of implants. Twelve rabbits were implanted with two implants per *Use of Statins in Dental Implantology and Their Impact on Osseointegration: Animal Studies DOI: http://dx.doi.org/10.5772/intechopen.108953*

tibia. Implants were in contact with the surface of the bone and bovine bone was used as graft material for gap filling. Animals were humanely sacrificed after 2 or 4 weeks. Results showed that bone-to-implant contact (BIC) was increased with UV treatment and SIM immersion on non-grafted sides and both BIC and bone area (BA) were increased on grafted sides. BIC or BA did not increase with both treatments in comparison with a single treatment. As data were collected at two different time points, results showed that BIC in the non-grafted sides did not differ significantly among UV- and/or SIM-treated groups, but BA was significantly different among groups. Ultraviolet or simvastatin treatments on SLA titanium implants accelerated osseointegration in tibias with or without xenogenic bone graft materials. Joint implementation of both treatments did not show significant positive effects [27].

Dundar and Bozoglan conducted their research on 16 female rats during a 4-week experimental trial. The subject was divided into two groups: a test group (*n* = 8) that received local simvastatin and a control group (*n* = 8) that did not receive simvastatin treatment. A titanium implant was surgically implanted into the tibial metaphysis of all 16 animals. Ethanol solution in the amount of 100 μl containing 5 mg simvastatin was applied to the bone sockets before implantation. Results for bone-implant contact (BIC) showed no statistically significant differences among test and control groups with regard to implant osseointegration (*p* > 0.05) [28].

Apostu et al. evaluated and compared the effects of different treatments (simvastatin, alendronate, and tibolone) on improved osseointegration of titanium implants. Research was conducted on 80 female albino Wistar rats evenly divided into five groups: Group 1 underwent ovariectomy, group 2 underwent false ovariectomy, group 3 underwent ovariectomy and alendronate treatment, group 4 underwent ovariectomy and simvastatin treatment, and group 5 underwent ovariectomy and tibolone treatment. Three months post-ovariectomy, the authors performed bilateral titanium intramedullary nailing (Ti90A16V4 alloy nails) in all groups followed by a 12-week oral administration of alendronate (3 mg/kg twice a week), simvastatin (5 mg/kg daily), or tibolone (5 mg/kg daily). Micro CT, mechanical pull-out test, histology, and bone serum markers were examined after 12-week oral treatment. Upon review of all examination results, the authors concluded that the initial hypothesis that simvastatin, alendronate, and tibolone enhance osseointegration in ovariectomized rats with intramedullary titanium implants has been accepted. Tibolone showed the best results out of three treatments [33].

### **4. Pharmacokinetics of simvastatin**

The chemical structure of all statins consists of the pharmacophore and its moiety containing a ring system with different substituents. The pharmacophore is shared among all statins, and it is a dihydroxyheptanoic acid segment that is very similar to the HMGCoA substrate [34]. The ring system consists of a complex hydrophobic structure covalently linked to the pharmacophore and it is involved in binding interactions with the HMG-CoA reductase enzyme [35]. There are different kinds of statins, which differ from each other in their hydrophobic ring structure and its substituents, covalently linked to the HMG-like moiety. These differences in structure affect the pharmacological properties of the statins [36].

The lipophilicity of the statins is considered important since the hepatoselectivity of the statins is related to their degree of lipophilicity. The higher the lipophilicity of statins, the greater level of exposure it gets to non-hepatic tissues, while the

more hydrophobic statins have a tendency to be more selective for the liver, whereas lipophilic statins passively and nonselectively diffuse into both hepatocytes and non-heptatocytes. The more hydrophobic statins largely rely on active transport into hepatocytes to exert their effects [37].

There are two forms of statins, lactone (inactive) and open-ring hydroxy acid (active) forms. The HMG-like moiety that all statins are in the inactive form as a lactone. Simvastatin and lovastatin are administered as lactone prodrugs and subsequently transformed into active metabolites. The remaining statins become in their active form as a β-hydroxy acid. *In vivo*, lactone statins are hydrolyzed to their hydroxy acid pharmacophores in the liver to achieve pharmacological activity [38].

We can divide statins into two groups: naturally or fungal-derived (type 1) and synthetic (type 2). One of the main differences between the type 1 and type 2 statins is the replacement of the fluorophenyl group of type 2 statins with the butyryl group in type 1 statins. These specific groups cause additional polar interactions and stronger and tighter binding to the HMGR enzyme. Functionally, the methylethyl group attached to the central ring of the type 2 statins replaces the decalin of the type 1 statins. The butyryl group of the type 1 statins occupies a region similar to the fluorophenyl group present in the type 2 inhibitors [39].

The hepatoselectivity is very important factor in liposolubility of the statins and their inhibitory effect on HMG-CoA reductase. Lipophilic statins enter the hepatocytes through passive diffusion, whereas hydrophilic statins undergo a carriermediated membrane [40].

Hydrophilicity depends on a transport process that takes the drug from the portal blood into hepatocytes using anion-transporting polypeptides (OATP). That molecules give better potential and selectivity for the liver cells. Hydrophilic statins such as rosuvastatin and pravastatin—have higher potential to the liver metabolism, because they harder way of entering other tissues as lipophilic statins do. However, the balance between desired and undesired effects of lipophilic and hydrophilic statins remains not clearly established [41].

### **5. Effect of statin on bone metabolism**

The bone tissue is a very dynamic formation that is always remodeled by bone cells osteoclasts and bone-forming osteoblasts.

Osteoblast cells are derived from mesenchymal stem cells and osteocytes derived from terminally differentiated osteoblasts [42, 43].

The biggest amount of lipids is present in bone marrow, and the lowest concentration of them in bone mineral matrix. Human bone contains 28–84% of neutral lipids, and only less than 3% of phospholipids [44].

Cholesterols have function in bone metabolism, in which membrane signal transducing platforms and play crucial roles in RANK-RANKL signal transduction during osteoclastogenesis.

High cholesterol levels also increase bone metabolism. High fat diets in mice caused osteoclastogenesis, and decrease in bone mass. The high-fat-fed antigeninduced arthritis (AIA) model also suggested that enhanced cathepsin K-positive osteoclasts contributed to more severe deterioration of the joints than in normal-dietfed AIA rabbits [45–47].

Cellular cholesterol has important role in cellular metabolism of macrophages pathways. Macrophages have the same origin as osteoclasts. The low-density

*Use of Statins in Dental Implantology and Their Impact on Osseointegration: Animal Studies DOI: http://dx.doi.org/10.5772/intechopen.108953*

lipoprotein receptor (LDLR) on macrophages promotes the internalization of ApoBcontaining lipoprotein, resulting in high levels of intracellular cholesterol [48, 49].

Osteoporosis is an epidemic throughout the world and is associated with trauma fractures in the vertebral spine, femoral neck, and distal radius. Specifically, postmenopausal osteoporosis is connected with pathological bone fractures. That is very often a disease in elderly women. It is typically associated with low bone mass and poor bone density.

Bisphophonates, selective estrogen receptor modulators, calcitonin, and vitamin D analogues are most usefully drugs for osteoporosis. They can also stop further bone loss. All of these drugs are inhibitors of bone resorption that act mainly to stabilize bone mass. It is hard to say if they are also osteoinductive [50, 51].

Osteoporosis and atherosclerosis share the tendency to accelerate after menopause; both diseases are promoted by inflammatory processes, and many aspects of arterial calcification and bone formation are similar [52]. The relationship between osteoporosis and atherosclerosis is supported by the observation that the progression of aortic calcification is most severe in women with the most severe metacarpal bone loss. Factors that may promote both processes include estrogen deficiency and increased concentrations of proinflammatory cytokines, such as IL-1, IL-6, and TNF-a [49, 50].

### **6. Conclusion**

A review of the results from the available literature shows that statins have a future in the use within oral surgery procedures and implantology where their osteogenic effect is most pronounced and their influence on the increase of the volume of newly formed bone and contact between implants and bone. Although studies have been conducted on small animals we believe that the potential of statins in bone formation is also high in humans. One of the studies also demonstrated the effectiveness of statins on bone fracture regeneration. We believe that local use of a statin applied to the bone bed of the implant, as well as topical application of a liquid statin to the implant surface, shows better osseointegration potential of the implant, as well as better contact of the implant with the more newly formed bone. A better effect on the soft tissues around the implant is also visible. It is possible that local statins increase level of bone morfogenic protein-2 (BMP-2) in bone metabolism, which affects higher level of newly formed bone. Future studies should establish safe and effective clinical protocols for statin application to promote osseointegration.


**Hydration and Setting Behaviour of Strontium Aluminate Cements**

Hydration of cement generally means complex changes and reactions which occur when the cement paste is prepared by mixing of anhydrous cement with water. Setting means stiffening without significant development of compressive strength which typically occurs within a few hours after mixing of cement with water. Hardening process means gradual significant development of compressive strength during curing in applied environmental conditions (storage in air or water, temperature) [263,265,270].

As was already mentioned in Chapter 2.6, cement slurries are complex reactive systems. They continuously change, physically and chemically. The microstructural and chemical evolution of cement slurry from the first minutes after mixing of cement powder with water until the beginning of setting can be observed by a variety of physicochemical methods including thermal analysis calorimetry [286-393], X-ray diffraction analysis [386,394,744], infrared Raman and Mössbauer spectroscopy [386,395,396], electron microscopy [273,275,394-399] as well as via liquid phase analysis [400,401], porosity and specific surface of cement stone measurement [402], ultrasonic pulse velocity [403-406], impedance spectroscopy measurement [407,408] and electrical conductivity/ resistivity measurement [409,410].

The knowledge of the setting characteristics of concrete is quite important in the field of concrete construction. They will help in scheduling of various stages involved in concrete construction operations such as transporting, placing, compacting and finishing of concrete. This information is a necessity when deciding whether to use a retarding admixture or accelerator or not [411].

The introduction of superplasticizers in early 1960s had great effect on the development in concrete technology. Superplasticized cement can be prepared with lower water to cement ratio, has improved workability, high strength and high durability without affecting the setting and hardening behaviour. In chemical terms, superplasticizers are organic polyelectrolytes which belong to the category of polymeric dispersants. Today, superplasticizers are considered as an integral component of High-Performance concretes [412].

ASTM C494 recognizes the following classes of superplasticizers [412]:

**Figure 33.** Particle size distribution of strontium aluminate clinker [379].

The specific surface, the particle size distribution (Chapter 3.5 and Chapter 6.1.2), the content of major and minor clinker phases (Chapter 2.5) in cement are the main parameters which can be used for the evaluation of quality of strontium aluminate clinker similarly to other binders such as AC and PC. These parameters define the proportion of fine and coarse particles in cement. This proportion controls the water demand, the setting and hydration reactions

128 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

**Figure 34.** The clinker phase (Sr3A, SrA, SrA2 and SrA6) and alumina (a) and strontium aluminate clinker with high con‐

Therefore, low firing temperature or rough milling procedure can be used in order to reduce initial high reactivity of SrA cement with water. The phosphorescence of calcinate can be ap‐ plied to evaluate the firing process (estimate the amount of unrecated alumina, Fig.34). Fur‐ thermore, the phosphorescence under UV light can be used for marking of cement or for

**6. Clinker quality evaluation**

tent of glassy phase (b) under visible and UV light.

preparation of cement layer or concretes of special properties.

[381-385].

© 2014 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Further sub-classifications of superplasticizers is also used and refers to the first, second and third generation of products.

The effect of superplasticizers' chemical structure on their efficiency in cement pastes was investigated by Janoska-Rekans [413]. The efficiency of industrial superplasticizers increases with the molecular weight of the superplasticizer polymer as well as with its mass fraction in considered sample. The efficiency of a superplasticizer increases with its hydrophilicity. The hydrophilic nature of the superplasticizer polymers can be measured as the ratio of ethers to esters.

General effect of admixtures such as silica fume, metakaolinite, flay ash and blast-furnace slag is the retardation of setting time of high-strength concrete [411]. Regarding limestone, the higher the limestone fines content in the mix, the shorter the initial and final setting times of concrete [414,415].

## **1. Analysis of hydration products**

The compounds formed during 28 days of hydration of strontium aluminate clinker were investigated by X-ray diffraction analysis (Fig.1). The cubic tri-strontium aluminate hexahy‐ drate phase (Sr3AH6) and the high alumina gel phase (AH3 gel) are recognized as the main products of hydration:

$$\text{3SrO} \times \text{Al}\_2\text{O}\_3 + \text{12 H}\_2\text{O} \to \text{3SrO} \times \text{Al}\_2\text{O}\_3 \times \text{6H}\_2\text{O} + \text{2Al}\_2\text{O}\_3 \times \text{3H}\_2\text{O} \tag{1}$$

**Figure 1.** Hydration of strontium aluminate clinker upon the first 28th days hydration [379].

and TG-DTA results [379].

**Figure 2.** Course of hydration of strontium aluminate cement. The figure was constructed via the combination of XRD

Hydration and Setting Behaviour of Strontium Aluminate Cements 131

**Figure 3.** X-ray diffraction analysis upon early stage of hydration of strontium aluminate clinker.

That enables to calculate the theoretic water to cement ratio for the hydration of strontium aluminate cement to be 0.36. SrAH7-10 hydrate and gibbsite (*γ*-AH3) appear after 7 and 14 days of hydration, respectively. The rate of the hydration process is significantly reduced after 14 days and the sample still contains about 20 % of unhydrated strontium aluminate phase in the 28th day of hydration (Fig.2).

The phase composition of strontium aluminate cement during the first 24 hours of hydration process is shown in Fig.3. These data confirm that tri-strontium aluminate hexahydrate is the only crystalline hydration product during early stages of hydration of strontium aluminate clinker and the initial rate of hydration is very fast as the results from calorimetric measure‐ ments show (Chapter 5.2). From this reason some important compounds improving the reactivity of strontium aluminate cement must be used in order to reach better workability (Chapter 5.4).

The infrared spectra (Fig.3) show sharp absorption band at 3664 cm-1, which is related to the stretching of OH groups of Sr3AH6. The dehydration of this phase shows sharp endothermic peak at the temperature of 262 °C on TG-DTA and EGA (Fig.5). The test piece area decreases in about 6.0 % during this process (Fig.28 in Chapter 4). The dehydration of the gel phase shows an endothermic effect on DTA at the temperature of 198 °C, but the peak intensity and the temperature decrease with the time of hydration.

**Figure 1.** Hydration of strontium aluminate clinker upon the first 28th days hydration [379].

Further sub-classifications of superplasticizers is also used and refers to the first, second and

130 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

The effect of superplasticizers' chemical structure on their efficiency in cement pastes was investigated by Janoska-Rekans [413]. The efficiency of industrial superplasticizers increases with the molecular weight of the superplasticizer polymer as well as with its mass fraction in considered sample. The efficiency of a superplasticizer increases with its hydrophilicity. The hydrophilic nature of the superplasticizer polymers can be measured as the ratio of ethers to

General effect of admixtures such as silica fume, metakaolinite, flay ash and blast-furnace slag is the retardation of setting time of high-strength concrete [411]. Regarding limestone, the higher the limestone fines content in the mix, the shorter the initial and final setting times of

The compounds formed during 28 days of hydration of strontium aluminate clinker were investigated by X-ray diffraction analysis (Fig.1). The cubic tri-strontium aluminate hexahy‐ drate phase (Sr3AH6) and the high alumina gel phase (AH3 gel) are recognized as the main

That enables to calculate the theoretic water to cement ratio for the hydration of strontium aluminate cement to be 0.36. SrAH7-10 hydrate and gibbsite (*γ*-AH3) appear after 7 and 14 days of hydration, respectively. The rate of the hydration process is significantly reduced after 14 days and the sample still contains about 20 % of unhydrated strontium aluminate phase in the

The phase composition of strontium aluminate cement during the first 24 hours of hydration process is shown in Fig.3. These data confirm that tri-strontium aluminate hexahydrate is the only crystalline hydration product during early stages of hydration of strontium aluminate clinker and the initial rate of hydration is very fast as the results from calorimetric measure‐ ments show (Chapter 5.2). From this reason some important compounds improving the reactivity of strontium aluminate cement must be used in order to reach better workability

The infrared spectra (Fig.3) show sharp absorption band at 3664 cm-1, which is related to the stretching of OH groups of Sr3AH6. The dehydration of this phase shows sharp endothermic peak at the temperature of 262 °C on TG-DTA and EGA (Fig.5). The test piece area decreases in about 6.0 % during this process (Fig.28 in Chapter 4). The dehydration of the gel phase shows an endothermic effect on DTA at the temperature of 198 °C, but the peak intensity and the

23 2 23 2 23 2 3 SrO×Al O +12 H O 3SrO×Al O ×6H O+2 Al O ×3H O ® (1)

third generation of products.

esters.

concrete [414,415].

products of hydration:

28th day of hydration (Fig.2).

temperature decrease with the time of hydration.

(Chapter 5.4).

**1. Analysis of hydration products**

**Figure 2.** Course of hydration of strontium aluminate cement. The figure was constructed via the combination of XRD and TG-DTA results [379].

**Figure 3.** X-ray diffraction analysis upon early stage of hydration of strontium aluminate clinker.

**Figure 4.** Infrared spectra of strontium aluminate clinker upon the first 28th days of hydration (a) and thermal treat‐ ment (b) [379].

The SEM pictures of strontium aluminate cement (**a**) and hydrated cement stone (**b**-**d**) during the first 28 days of hydration process are shown in Fig.6. Well-developed crystals of Sr3AH6 (**b**) precipitated and grew from supper-saturated liquid phase of cement slurry before setting. The hydration products usually formed during the setting do not occur in well-developed rhombic dodecahedron of Sr3AH6.

**Figure 6.** SEM pictures of strontium aluminate clinker (a) and hydrated cement stone after 3 (b) and 21(c) and 28(d)

Hydration and Setting Behaviour of Strontium Aluminate Cements 133

Fig.7 shows the heat flow in the combination with the heat of hydration of strontium aluminate cement (a) and calcium aluminate cement (b, Secar 51) during 50 hours of hydration process at the temperature of 25 °C. Fast evolution of heat immediately after mixing with water is typical for strontium aluminate cement while 10 hours long induction period was measured for calcium aluminate cement. There isn't any induction period observed hence the hydration of strontium aluminate cement starts immediately after mixing of strontium aluminate cement with water and the heat flow then asymptotically decreases to the baseline. The main hydration

reaction in calcium aluminate cement arises 13.5 hours after mixing with water.

**2. Hydration and activation energy of hydration**

days of hydration process [379].

**Figure 5.** Thermal analysis of hydrated sample of strontium aluminate clinker performed at the heating rate of 10 °C min-1 [379].

The SEM (Fig.6) picture of hydrated cement stone after 21 and 28 days of hydration shows well-developed Sr3AH6 crystals surrounded by kidney-shaped aggregates of SrAH7 [379].

**Figure 6.** SEM pictures of strontium aluminate clinker (a) and hydrated cement stone after 3 (b) and 21(c) and 28(d) days of hydration process [379].

## **2. Hydration and activation energy of hydration**

**Figure 4.** Infrared spectra of strontium aluminate clinker upon the first 28th days of hydration (a) and thermal treat‐

132 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

The SEM pictures of strontium aluminate cement (**a**) and hydrated cement stone (**b**-**d**) during the first 28 days of hydration process are shown in Fig.6. Well-developed crystals of Sr3AH6 (**b**) precipitated and grew from supper-saturated liquid phase of cement slurry before setting. The hydration products usually formed during the setting do not occur in well-developed

**Figure 5.** Thermal analysis of hydrated sample of strontium aluminate clinker performed at the heating rate of 10 °C

The SEM (Fig.6) picture of hydrated cement stone after 21 and 28 days of hydration shows well-developed Sr3AH6 crystals surrounded by kidney-shaped aggregates of SrAH7 [379].

ment (b) [379].

min-1 [379].

rhombic dodecahedron of Sr3AH6.

Fig.7 shows the heat flow in the combination with the heat of hydration of strontium aluminate cement (a) and calcium aluminate cement (b, Secar 51) during 50 hours of hydration process at the temperature of 25 °C. Fast evolution of heat immediately after mixing with water is typical for strontium aluminate cement while 10 hours long induction period was measured for calcium aluminate cement. There isn't any induction period observed hence the hydration of strontium aluminate cement starts immediately after mixing of strontium aluminate cement with water and the heat flow then asymptotically decreases to the baseline. The main hydration reaction in calcium aluminate cement arises 13.5 hours after mixing with water.

setting time of strontium aluminate clinker is significantly reduced by increasing

Hydration and Setting Behaviour of Strontium Aluminate Cements 135

Figure 9. Tan delta for strontium aluminate clinker set at the temperature of 0 (a), 10 (b), 30 (c) and 50 °C (d) and influence of temperature on the setting time (f). The data for Secar 51 at 25 °C are shown

**Figure 9.** Tan delta for strontium aluminate clinker set at the temperature of 0 (a), 10 (b), 30 (c) and 50 °C (d) and

influence of temperature on the setting time (f). The data for Secar 51 at 25 °C are shown in (e).

Fast evolution of heat after mixing with water without the induction period is a disadvantage of strontium aluminate cement. In order to improve the cement workability

Fast evolution of heat after mixing with water without the induction period is a disadvantage of strontium aluminate cement. In order to improve the cement workability the influence of some organic and inorganic compounds on the process of hydration was investigated by isothermal calorimetry. The formation of strontium chelates or buffer with organic acids, such as acetic and citric acid, or the formation of diffusion barrier on the surface of strontium

aluminate grains via the introduction of sodium sulfate or boric acid are supposed.

temperature.

in (e).

**4. Improving mixture workability**

**4. Improving mixture workability**

**Figure 7.** Heat flow and heat of hydration of strontium [379] (a) and calcium aluminate cement (b).

After the first 50 hours of hydration the heat flow of both cements already drops down to the baseline, but still produces 0.21 and 0.11 mW g-1 for strontium aluminate and calcium alumi‐ nate cement, respectively.

**Figure 8.** Arrhenius plot for the hydration of strontium aluminate cement.

The calorimetric assessments at the temperature of 15, 20 and 25 °C were applied in order to investigate the activation energy of hydration of strontium aluminate cement (Fig.8(a)). The apparent activation energy and the frequency factor of the process were calculated from the Arrhenius plot to be 51 kJ∙mol-1 and 2.55∙106 s-1 (b), respectively. The D4 kinetic equation was evaluated as the most probable mechanism of the process of hydration.

#### **3. Setting behaviour and influence of temperature**

The measurement of storage modulus, loss modulus and damping factor (*tan* **θ**) were per‐ formed in order to evaluate the behaviour of strontium aluminate slurry prepared with the water to cement ratio of 0.3 at different temperatures. The results (Fig.9) indicate that the setting time of strontium aluminate clinker is significantly reduced by increasing temperature.

setting time of strontium aluminate clinker is significantly reduced by increasing

Figure 9. Tan delta for strontium aluminate clinker set at the temperature of 0 (a), 10 (b), 30 (c) and 50 °C (d) and influence of temperature on the setting time (f). The data for Secar 51 at 25 °C are shown **Figure 9.** Tan delta for strontium aluminate clinker set at the temperature of 0 (a), 10 (b), 30 (c) and 50 °C (d) and influence of temperature on the setting time (f). The data for Secar 51 at 25 °C are shown in (e).

#### **4. Improving mixture workability 4. Improving mixture workability**

in (e).

temperature.

After the first 50 hours of hydration the heat flow of both cements already drops down to the baseline, but still produces 0.21 and 0.11 mW g-1 for strontium aluminate and calcium alumi‐

**Figure 7.** Heat flow and heat of hydration of strontium [379] (a) and calcium aluminate cement (b).

134 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

The calorimetric assessments at the temperature of 15, 20 and 25 °C were applied in order to investigate the activation energy of hydration of strontium aluminate cement (Fig.8(a)). The apparent activation energy and the frequency factor of the process were calculated from the

The measurement of storage modulus, loss modulus and damping factor (*tan* **θ**) were per‐ formed in order to evaluate the behaviour of strontium aluminate slurry prepared with the water to cement ratio of 0.3 at different temperatures. The results (Fig.9) indicate that the setting time of strontium aluminate clinker is significantly reduced by increasing temperature.

s-1 (b), respectively. The D4 kinetic equation was

nate cement, respectively.

**Figure 8.** Arrhenius plot for the hydration of strontium aluminate cement.

evaluated as the most probable mechanism of the process of hydration.

**3. Setting behaviour and influence of temperature**

Arrhenius plot to be 51 kJ∙mol-1 and 2.55∙106

disadvantage of strontium aluminate cement. In order to improve the cement workability Fast evolution of heat after mixing with water without the induction period is a disadvantage of strontium aluminate cement. In order to improve the cement workability the influence of some organic and inorganic compounds on the process of hydration was investigated by isothermal calorimetry. The formation of strontium chelates or buffer with organic acids, such as acetic and citric acid, or the formation of diffusion barrier on the surface of strontium aluminate grains via the introduction of sodium sulfate or boric acid are supposed.

Fast evolution of heat after mixing with water without the induction period is a

**Figure 10.** Calorimetry of strontium aluminate cement with acetic acid, citric acid, sodium sulfate and boric acid.

The effect of sulfates on the course of hydration of strontium aluminate cement is discussed in Chapter 8.2, but the addition of gypsum up to 5 % can improve the behaviour of cement during the hydration.

**Figure 11.** Early age volume shrinkage of strontium aluminate cement slurry.

**6. Hydration of other phases in SrO-Al2O3 system**

for more rapid diffusion of water.

strain in Sr3Al2O6.

time of 60 hours.

cement stone after setting.

The tristrontium aluminate (Sr3A) phase is more reactive than tricalcium aluminate (Ca3A). There are two possible reasons for increased reactivity of tristrontium aluminate [8,416,417]:

Hydration and Setting Behaviour of Strontium Aluminate Cements 137

**1.** Increased size of Sr2+cations increases the size of channels within the Al6O8 rings allowing

**2.** Considerable overbonding at three Sr2+sites occurs suggesting that there is considerable

The isothermal calorimetric experiments on the hydration of other strontium aluminate phases such as tri-strontium aluminate, strontium dialuminate and strontium hexaaluminate com‐ pared to strontium aluminate at the temperature of 25 °C are shown in Fig.12. The calorimetric data show that cements based on tri-strontium aluminate phase have short induction periods. The main and second hydration effect arise at the time of 4 and 48 h after mixing with water. The main hydration effect drops down to the baseline at the time of 10 h and the second at the

2 Hydration is defined as a reaction of inorganic binder with water accompanied by setting and hardening. Setting is spontaneous conversion of cement slurry into solid body. Hardening is a process of gradual increasing of strength of

#### **5. Chemical shrinkage**

Chemical shrinkage1 is defined as the absolute (internal) volume change of cement paste that results from the hydration of cementitious materials. Chemical shrinkage of strontium aluminate cement was evaluated using the pycnometric measuring technique described by Zhang at al. [674].

The shrinkage of cement slurry after mixing with water is shown in Fig.11. There are two linear parts, which can be extrapolated to the cross point at the time of 5.2 hours after mixing with water with corresponding volume shrinkage of 2.7 cm3 /100g.

This change in the shrinkage direction should be explained as the turn of the hydration (chemical) shrinkage to the setting shrinkage2 (7.3 cm3 /100g). The cross point appearing at the time of 77.2 hours after mixing of SrAC with water is related to the formation of SrAHx hydrate (where x=7-10, please consult with Fig.2) [379]. The total volume shrinkage of cement slurry reaches about 10 cm3 /100g after 13 days of hydration.

1 The deeper discussion on the chemical shrinkage can be found in Chapter 8.

**Figure 11.** Early age volume shrinkage of strontium aluminate cement slurry.

**Figure 10.** Calorimetry of strontium aluminate cement with acetic acid, citric acid, sodium sulfate and boric acid.

136 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

during the hydration.

Zhang at al. [674].

reaches about 10 cm3

**5. Chemical shrinkage**

water with corresponding volume shrinkage of 2.7 cm3

1 The deeper discussion on the chemical shrinkage can be found in Chapter 8.

(chemical) shrinkage to the setting shrinkage2

The effect of sulfates on the course of hydration of strontium aluminate cement is discussed in Chapter 8.2, but the addition of gypsum up to 5 % can improve the behaviour of cement

Chemical shrinkage1 is defined as the absolute (internal) volume change of cement paste that results from the hydration of cementitious materials. Chemical shrinkage of strontium aluminate cement was evaluated using the pycnometric measuring technique described by

The shrinkage of cement slurry after mixing with water is shown in Fig.11. There are two linear parts, which can be extrapolated to the cross point at the time of 5.2 hours after mixing with

This change in the shrinkage direction should be explained as the turn of the hydration

time of 77.2 hours after mixing of SrAC with water is related to the formation of SrAHx hydrate (where x=7-10, please consult with Fig.2) [379]. The total volume shrinkage of cement slurry

/100g after 13 days of hydration.

(7.3 cm3

/100g.

/100g). The cross point appearing at the

## **6. Hydration of other phases in SrO-Al2O3 system**

The tristrontium aluminate (Sr3A) phase is more reactive than tricalcium aluminate (Ca3A). There are two possible reasons for increased reactivity of tristrontium aluminate [8,416,417]:

The isothermal calorimetric experiments on the hydration of other strontium aluminate phases such as tri-strontium aluminate, strontium dialuminate and strontium hexaaluminate com‐ pared to strontium aluminate at the temperature of 25 °C are shown in Fig.12. The calorimetric data show that cements based on tri-strontium aluminate phase have short induction periods. The main and second hydration effect arise at the time of 4 and 48 h after mixing with water. The main hydration effect drops down to the baseline at the time of 10 h and the second at the time of 60 hours.

2 Hydration is defined as a reaction of inorganic binder with water accompanied by setting and hardening. Setting is spontaneous conversion of cement slurry into solid body. Hardening is a process of gradual increasing of strength of cement stone after setting.

The heat flow of strontium aluminate phases is 0.58 (70 h), 0.21 (50 h) and 0.08 mW g-1 (50 h) for tri-strontium aluminate, strontium aluminate and strontium dialuminate phase after the

Hydration and Setting Behaviour of Strontium Aluminate Cements 139

Tri-strontium aluminate hexahydrate is the only crystalline hydration product that can be

The results of thermal analysis of strontium aluminate clinker after the hydration are shown in Fig.15(a). The TG-DTA plot confirms that tri-strontium aluminate hexahydrate is the only hydration product of hydration of Sr3A clinker. Please refer to Chapter 6.5 for the discussion

The stretching of OH groups at 3663 cm-1 in Sr3AH6 is the most characteristic feature in infrared spectrum of hydrated cement stone (Fig.15(b)). The deformation mode is located at the wavenumber of 1757 cm-1. The bands located at 786 and 502 cm-1 are most probably the composed bands of symmetric and antisymmetric stretching of =Al-OH groups [418,419,422] and the characteristic frequency of Al-O-Al stretching of AlO6 octahedra [420,421,422],

SEM pictures of hydrated cement stone of ground tristrontium aluminate (Sr3A) clinker are

**Figure 14.** Ground clinker prepared from tri-strontium aluminate (a) and hydration products (b).

of mechanism of thermal dehydration of tri-strontium aluminate hexahydrate.

first 50 hours of hydration, respectively.

recognized by X-ray diffraction analysis (Fig14).

**Figure 15.** TG-DTA (a) and FT-IR (b) of hydrated cement stone.

respectively.

shown in Fig.16.

**Figure 12.** Heat flow and heat of hydration of tri-strontium aluminate (a), strontium aluminate (b), strontium dialumi‐ nate (c) and strontium hexaaluminate (d) at the temperature of 25 °C.

The heat of hydration decreases with decreasing strontium oxide/ aluminum oxide in the phase (Fig.13). According to the decrease of heat of hydration, the strontium aluminate phases should be ordered as follows:

Sr3A >> SrA >> SrA2 > SrA6.

It seems to be the sigmoidal dependence of heat on hydration, where the inflexion point corresponds to the strontium aluminate phase.

**Figure 13.** Hydration heat of strontium aluminate phases after the first 50 hours of hydration.

The heat flow of strontium aluminate phases is 0.58 (70 h), 0.21 (50 h) and 0.08 mW g-1 (50 h) for tri-strontium aluminate, strontium aluminate and strontium dialuminate phase after the first 50 hours of hydration, respectively.

Tri-strontium aluminate hexahydrate is the only crystalline hydration product that can be recognized by X-ray diffraction analysis (Fig14).

**Figure 14.** Ground clinker prepared from tri-strontium aluminate (a) and hydration products (b).

The results of thermal analysis of strontium aluminate clinker after the hydration are shown in Fig.15(a). The TG-DTA plot confirms that tri-strontium aluminate hexahydrate is the only hydration product of hydration of Sr3A clinker. Please refer to Chapter 6.5 for the discussion of mechanism of thermal dehydration of tri-strontium aluminate hexahydrate.

**Figure 15.** TG-DTA (a) and FT-IR (b) of hydrated cement stone.

**Figure 12.** Heat flow and heat of hydration of tri-strontium aluminate (a), strontium aluminate (b), strontium dialumi‐

138 Strontium Aluminate - Cement Fundamentals, Manufacturing, Hydration, Setting Behaviour and Applications

The heat of hydration decreases with decreasing strontium oxide/ aluminum oxide in the phase (Fig.13). According to the decrease of heat of hydration, the strontium aluminate phases should

It seems to be the sigmoidal dependence of heat on hydration, where the inflexion point

**Figure 13.** Hydration heat of strontium aluminate phases after the first 50 hours of hydration.

nate (c) and strontium hexaaluminate (d) at the temperature of 25 °C.

corresponds to the strontium aluminate phase.

be ordered as follows:

Sr3A >> SrA >> SrA2 > SrA6.

The stretching of OH groups at 3663 cm-1 in Sr3AH6 is the most characteristic feature in infrared spectrum of hydrated cement stone (Fig.15(b)). The deformation mode is located at the wavenumber of 1757 cm-1. The bands located at 786 and 502 cm-1 are most probably the composed bands of symmetric and antisymmetric stretching of =Al-OH groups [418,419,422] and the characteristic frequency of Al-O-Al stretching of AlO6 octahedra [420,421,422], respectively.

SEM pictures of hydrated cement stone of ground tristrontium aluminate (Sr3A) clinker are shown in Fig.16.

**Chapter 6**

**Applications of Strontium Aluminate Cements**

mentioned.

**1. Refractory materials**

**• Non-oxide ceramics:** carbides (SiC1

named the new substance as carborundum [429].

refractory materials and products can be recognized [423].

The applications such as dense or thermal insulating refractory materials, the preparation of seawater resistance concretes and as the protection against X-ray and gamma ration are supposed for strontium aluminate cements [12,14]. The option to use strontium aluminate cement for the preparation of MDF composites as was described in Chapter 6.4 is also

**Refractory products** (**refractories**) possess the ability to resist high temperatures without physical or chemical destruction, the corresponding properties are termed as **refractoriness**. These materials can be classified according to their temperature resistance, chemical compo‐ sition, porosity, etc. According to the most general viewpoint the ceramic and non-ceramic

Based on the chemical composition, the following types of refractory materials can be specified:

**• Oxide ceramics:** are an extensive group of materials based on one or few oxides (SiO2, Al2O3, Cr2O3, ZrO2, MgO and CaO) and their stable compounds (ZrO∙SiO2, MgO∙Cr2O3, MgO∙Al2O3, 3Al2O3∙2SiO2...). The silica refractory products, alumina-silica refractory products with different content of alumina, basic refractory products, alumina-zirconiasilica refractory products, alumina-chromic oxide-zirconia-silica refractory products, etc., are the most common examples of these materials. The alumina silicate refractories are extensively used in metallurgical, ceramic and glass industries. These materials are made primarily of refractory and kaolinitic clays, which are used both in crude and grog forms [424,425]. Spinel (MgO⋅Al2O3) is very attractive as refractory material in heavy industries because of its high melting point, low thermal expansion, considerable hardness, high resistance to chemical attack, favorable chemical stability, and good thermal spalling [426].

[433-435], BN [436], TiN [437], AlN [438], SiAlONs [439],...) silicides (MoSi2 [440,441]) can be considered as the most common types. Among the physico-chemical properties of

1 The formation of SiC was firstly described by Berzelius in 1810 and 1821, but silicon carbide was latterly rediscovered by Despretz, Schützenberger and Moissan. The preparation of SiC on a large scale was managed by Acheson is 1891 who

> © 2014 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

material the kind of applied bound is an important factor for these materials.

[427-429], B4C [429-431], Al4C3 [432],...), nitrides (Si3N4

**Figure 16.** Tri-strontium aluminate hydrated cement stone after 72 h of hydration at 25 °C.

The hydrogarnet phase seems to be the only hydration product of Sr3A (Fig.14), but the microphotographs show two main crystalline forms of the main product of hydration: icositetrahedron and hexagonal plates. Icositetrahedron are early forms precipitated from supersaturated solution, while hexagonal shapes are formed during later stage of hydration process.

Therefore the hydration process of tristrontium aluminate clinker should be described by the following chemical equation:

$$\text{3SrO} \times \text{Al}\_2\text{O}\_3 + 6\text{ H}\_2\text{O} \to \text{3SrO} \times \text{Al}\_2\text{O}\_3 \times 6\text{H}\_2\text{O} \tag{2}$$

which corresponds to the theoretic *w*/*c* ratio of about 0.21. This value is lower than theoretic water to cement ratio (Eq.1) calculated for strontium aluminate clinker (0.36).