Accelerators compressive strength

Hemihydrate. The abiUty of plaster of Paris to readily revert to the dihydrate form and harden when mixed with water is the basis for its many uses. Of equal significance is the abiUty to control the time of rehydration in the range of two minutes to over eight hours through additions of retarders, accelerators, and/or stabilizers. Other favorable properties include its fire resistance, excellent thermal and hydrometric dimensional stabiUty, good compressive strength, and neutral pH. 

Brauer, Stansbury Flowers (1986) modified these cements in several ways. The addition of various adds - acetic, propionic, benzoic etc. -accelerated the set. The use of zinc oxide powders coated with propionic add improved mixing, accelerated set, reduced brittleness and increased compressive strength from 63 to a maximum of 72 MPa. The addition of plasticizing agents such as zinc undecenylate yielded flexible materials. Incorporation of metal powders had a deleterious effect and greatly increased the brittleness of these cements. The addition of fluorides was not very successful, for fluoride release was not sustained. 

Diaikanol aminoalkyl phenols as admixtures enhance the strength [675]. The additives are useful in very small amounts and do not affect the initial properties of the fluid. The strength additive does not cause set acceleration or early set strength enhancement but provides enhanced compressive strength of the cement in later stages. Addition of small amounts of potassium ferricyanide and nitrile-trimethyl phosphonic acid promotes the formation of complex compounds and thus increases the strength of cement rock [1771]. 

The data available on the effect of accelerators on the flexural and tensile strengths and the modulus of elasticity are limited [22, 30, 31] and are relevant only to calcium chloride and triethanolamine. The data generally point to either no effect or a slight reduction in all three properties. Also, in view of the increase in compressive strength, it is reasonable to assume that for a given compressive strength, the presence of calcium chloride or triethanolamine will reduce the flexural and tensile strengths and the modulus of elasticity. 

Mix no. Accelerator (%) (cement basis) Acceleration (%) (initial set) Compressive strengths (MPa) ... 

Compressive strength Tests conducted on cores extracted from test panels shot during routine quality control show that silica fume shotcrete produce consistently higher compressive strengths and lower permeability in the hardened shotcrete than shotcrete where accelerators were used. 

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... 

Accelerated cure compressive strengths 28-day compressive strength (MPa) (MPa) at age 16-17 h... 

Supercritical C02 (sc C02) is being used to accelerate the natural aging reactions (i.e., carbonation) of Portland cement. This treatment method alters the bulk properties of cement, producing profound changes in both structure and chemical composition. As a result of these changes, the mechanical and transport properties of these cements are also dramatically affected, and they display reduced porosity, permeability and pH, as well as increased density and compressive strength. 

There are several indications that the compressive strength does not depend solely on porosity. In general, procedures that accelerate early reaction and... 

Montmorillonite is an effective complex with the initiator in the polymerization of methyl methacrylate." It not only accelerates the polymerization but also improves such mechanical properties as hardness and compression strength. Pentabromobenzyl acrylate was mechano-polymerized in the presence of Mg(0H)2. The polymerization occurred at a reduced temperature and a flame retarded product was produced. 

Accelerated hydrolytic stability tests Indicate that the polyether-based urethane employed In this study In the preparation of the liner pads can successfully withstand contlntious Immersion In water at 3S C for 24 years. Under such an exposure, the pads are expected to lose approximately 20 percent of their original compressive strength. 

MPa, compressive strength 245-303 MPa, water sorption 0.5-0.7/cm ) considerably exceeded the minimum requirement of the specification for dental composite resins (37). If low concentrations are employed in the formulations especially with DEAPAA as accelerator, the cured composites are nearly colorless. No perceptible change occurs in the color of the specimens containing a UV absorber after 24 hours exposure to a UV light source. Because of the excellent overall physical properties, nearly colorless appearance and the potentially better biocompatibility, compositions using these accelerators should yield improved restoratives. 

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