Cement strength development

The classic approach to the cement strength development was to increase the alite and CjA content, as well as the fineness of cement. The increase of silica modulus to about 3 and use of some minor components, mainly barium and boron results in further cement properties enhancement. The rate of hardening of these cements [121-123] is increasing with their specific surface in the range 4,400-4,600 cm /g and with K2SO addition (1.5 %), according to Grzymek s patent [124]. 

In seventies, XXc, the studies aimed in the improvement of behte cements strength development were imdertaken. The two methods are apphed the first consists in the accelerahon of behte hydration, while the seeond one—in enhancing the content of ettringite formed. As it was explained in Sect. 9.3, the application of... 

Fegulated-set cement, called jet cement in Japan, is formulated to yield a controlled short setting time, <1 h, and very eady strength (73). It is a modified cement that can be manufactured in a conventional Pordand cement kiln. It incorporates set control and eady strength development components. 

The bond strength to enamel (2-6 to 9-9 MPa) is greater than that to dentine (1-5 to 4-5 MPa) (Wilson McLean, 1988). Bond strength develops rapidly and is complete within 15 minutes according to van Zeghbroeck (1989). The cement must penetrate the acquired pellicle (a thin mucous deposit adherent to all surfaces of the tooth) and also bond to debris of calciferous tooth and the smear layer present after drilling. Whatever the exact mode of bonding to tooth stmcture, the adhesion is permanent. The principles and mechanism of adhesion have already been discussed in Section 5.2. 

Cement strength and resistance to aqueous attack are also critically dependent on phosphoric add concentration, and there is an optimum concentration for the development of maximum strength and resistance to aqueous attack (Wilson et al., 1970a Wilson, Paddon Crisp, 1979). The effect is particularly critical when the phosphoric add liquid contains aluminium and zinc. 

Dental silicate cement is solely used for restoring anterior (front) teeth. It is probably the strongest purely inorganic cement and develops its strength rapidly. Although satisfactory in areas of the mouth washed by saliva it is... 

Beaudoin, J. J. Ramachandran, V. S. (1975). Strength development in magnesium oxychloride and other cements. Cement and Concrete, 5 (6), 617-30. 

Messing (1961) found that he could improve ZOE cements by adding 10 % polystyrene to the liquid. Strength developed more rapidly than in an unmodified but accelerated cement and after 24 hours reached 42 MPa compared with 36 MPa. 

A concrete with similar workability and strength development characteristics can be obtained at lower cement contents than a control concrete without adversely affecting the durability or engineering properties of the concrete. 

Fig. 2.19 Strength development of high-strength flowing concrete containing melamine-based superplasticizer compared to concrete made with 400 kg of normal Portland cement per m in the stiff to low workability ranges (25-100 mm slump). 

Two types of calcium nitrite-based corrosion inhibitors are currently marketed, viz. a set- and strength-accelerating type and a normal-setting type. The former increases the early strength development in concrete. This effect increases with the dosage. Both admixtures are compatible with all types of Portland cements and... 

A variety of admixtures and additives are used to accelerate strength development, cohesiveness, bond, freeze-thaw and abrasion resistance, and to reduce rebound. Most of the accelerating admixtures used probably act by precipitating as insoluble hydroxides or other salts - a form of false set. Conduction calorimetric studies show that their main effect on early strength is due to the action on the C3 A fraction of the cement. The reaction of... 

The lower water-cement ratio afforded by the use of a superplasticizer may be used to increase existing compressive strengths or to reduce cement content. Thus the use of superplasticizers may enable the precast producer to use lower cement content without reduction in mix workability and rate of strength development. The actual amount of cement reduction achieved will depend on the cement type used and the mix proportion used in the concrete. Previous work [63] indicates that even with low cement content (306 kg m 3) a normal dose of superplasticizer can accelerate 3- and 28-day strengths by 90% and 55%, respectively, over levels attained with a plain mix. Cement reductions in the range of 11-20% have been achieved in mixes with a cement content of 415 kg m, while maintaining desired strength... 

More substantial increases in the rate of strength development are obtained by the use of superplasticizers. As mentioned previously, because of the dramatic water reduction that can be achieved by the use of higher dosage of the superplasticizers, significant cement reduction or a change in the type of cement (from a high early Type 111 to a normal Type 1) is possible (Tables 7.28, 7.29 and 7.7). 

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