International Concrete Abstracts Portal

Blast furnace slags and pulverized fly ash have been used extensively as additives to ordinary portland cement (OPC) to make low-permeability pastes with adequate long-term strengths. These properties are a consequence of phase development in the matrix that proceeds nonuniformly because the OPC clinker and blending agent react at different rates. Also, sheaths of hydration products forming around anhydrous grains inhibit reaction. This complicates our interpretation of the properties of blended cement systems because phases observed as products on laboratory time scales are not necessarily representative of the steady state assemblages. The aqueous chemistry is also subject to time-dependent changes since solution composition is related to that of the coexisting solids. In some applications, it is necessary to predict long-term physicochemical properties. This can be achieved through modeling, based on sound scientific principles, and using as much information as realistic from immature systems. Paper describes progress in model development and verification.

Presents the latest publications dealing with the development and practical application of activated slag clinker-free concretes with special reference to less known papers and recent information. The finely ground slag, usually granulated blast furnace slag, is activated by the solution of sodium or potassium hydroxide, carbonate, or preferably silicate (soluble glass) of appropriate concentration and silicate modulus. The difference of microstructure between portland cement concrete and alkali-activated slag concrete and its consequences for their properties, especially for very high strengths and corrosion resistance, is discussed. The use of nonstandard aggregate and other industrial by-products, as well as the low costs of this type of concrete are presented. Examples of applications of alkali-activated slag concrete of different composition are given. Some problems connected with the present use of alkali-activated concrete are discussed together with the most promising applications for the future.

Hydration of cements containing the supplementary cementing materials fly ash (FA) and silica fume (SF) is discussed and compared with the hydration of ordinary portland cement (OPC). Early stage heats of hydration, changes in the chemistry of the solution (both at early stages, and later pore solution compositions), microstructural development, and pore structure are compared. The hydration rates normally follow the order: SF > OPC > FA. The complex hydration processes may be controlled so that the use of these cements enables development of materials having superior strength and durability.

The chemical resistance of alkali-activated slag pastes and mortars in chloride solutions was studied. The four basic slag-alkali binding materials were prepared using granulated blast furnace slag, copper slag, and a mix of both these components. NaOH and Na?2CO?3 were used as activators. Some pastes and mortars containing 10 percent active silica additive were also made. The mortars were cured in standard conditions as well as subjected to low-pressure steam curing. The chemical resistance of alkali-activated slag mortars was compared with the chemical resistance of OPC mortars. The water-to-solid ratio was kept constant at 0.40. The samples cured in water were considered as reference samples. It has been found that the alkali-activated slag binders are chemical resistant in chloride solutions. These results were found not only from chemical resistance in chloride solutions and compressive and flexural strength tests, but also from the SEM observations of microstructure. The difference between the chemical resistance of slag and OPC mortars is probably the consequence of phase composition and porosity of the hydration products

Presents data on selected properties of cement pastes and concretes containing peat fly ash as a supplementary cementing material. Reference concretes and cement pastes with pure portland cement and with coal fly ash were used. The tests were performed as comparison tests on pastes and concretes with or without an air-entraining agent. In addition, a superplasticizer and a water reducer were used in the pastes and concretes containing fly ashes. The fly ash contents used varied between 20 and 60 percent by mass of the total amount of binder. Tests on cement pastes showed that using peat fly ash or coal fly ash decreases the cracking tendency of a portland cement paste as measured by a shrinkage ring test method. No differences were observed between the pastes with peat fly ash or coal fly ash in this experiment. Drying shrinkage results show that concretes containing peat fly ash developed somewhat lower shrinkage values than the control mixtures containing coal fly ash. The strength, impermeability, and frost-resistance properties of concretes with peat fly ash did not essentially differ from those of coal fly ash concretes. The test data indicate that with proper mix design and choice of admixtures, peat fly ash could be used as a supplementary cementing material to produce a high-quality, frost-resistant concrete.