International Concrete Abstracts Portal

Describes chemical attack caused by a high concentration CaCl 2 solution and its preventive measures by the addition of a mineral admixture. Changes which occur in mechanical strengths and chemical properties in mortars with and without fly ash, blast furnace slag, and silica fume when immersed in a 30 percent CaCl 2 solution at different temperatures were investigated. Portland cement mortars seriously deteriorated at early ages of exposure to a high concentration CaCl 2 solution, its deterioration being associated with cracking and spalling on the surfaces of specimens. On the other hand, 10 percent silica fume and 50 percent blast furnace slag mortars showed a good resistance to calcium chloride attack, although 30 percent fly ash mortars slightly deteriorated at late ages of exposure. X-ray diffraction and differential thermal analysis indicated that the deterioration of portland cement mortars cause by the chemical attack of a high concentration CaCl 2 solution was attributed primarily to both the dissolution of calcium hydroxide and the simultaneous formation of a complex salt in the mortar. Thus, the combined effect of a decrease in calcium hydroxide content and a reduced chloride ion permeability by the addition of a mineral admixture effectively improved the resistance of mortar to calcium chloride attack.

Describes test results obtained on the heat of hydration, strength development, hydration products, pore structure, and combined water of blended cements with high fineness and large amounts of ground granulated blast furnace slag (GGBS) and discusses the relationship between them, comparing them with ordinary portland cement (OPC) and blended cement with smaller amounts of GGBS. The following conclusions were drawn from this study. 1. The heat of hydration of blended cement with over 70 percent content of GGBS reduces significantly. The blended cement incorporating a large amount of GGBS with high fineness can have the properties of lower heat of hydration and relatively high compressive strength required for massive concrete generally used in Japan. 2. The blended cement with high fineness and high content of GGBS results in a more compact pore structure than OPC due to the formation of finer hydration products.

In Japan, the use of blast furnace slag is a specified measure for reducing alkali-silica reaction (ASR) expansion in concrete. Most of the studies on the effect of blast furnace slag on reducing ASR expansion have been carried out with mortar tests; few studies have been carried out on the relationship between expansions in mortar and concrete. The studies on concrete containing different contents of reactive aggregate and blast furnace slag have been very limited. A proper method for estimating the effect of slag on reducing expansion has not been established. In this study, the expansion characteristics of mortar made using reactive aggregate and slag cement and the effect of replacement of portland cement by slag to reduce the expansion of concrete due to ASR were investigated. The effect of blast furnace slag for reducing expansion due to ASR is described from the viewpoint of dilution, stabilization, and immobilization of alkali. The pessimum conditions of expansion in concrete containing different reactive aggregate contents were studied. The expansion of concrete with 100 percent reactive fine aggregate was the largest. In addition, in the concrete with 100 percent reactive coarse aggregate and 50 percent slag, the limit value of total alkali content was estimated, as 8.0 kg/m 3 without considering the alkali content in slag, and as 9.0 kg/m 3 when the alkali content in slag is taken into consideration.

The granulated blast furnace slags or nonferrous slags are the main component of the alkali activated slag cementitious materials. The calcium silica hydrates (C-S-H type) of low basicity, hydrogarnets, and sodium zeolites form as the alkali activated slag hydration products. Their structure and properties indicate that they can play an essential role in the immobilization of some elements. The microstructure of alkali activated slag pastes shows a higher gel pores content as compared with normal portland cement pastes and, simultaneously, significantly lower capillary pores fraction. The properties of alkali activated slag pastes in the presence of Zn, Cd, Cr, and Pb ions were studied. The results of the strength tests, as well as the data relating to the phase composition and microstructure of pastes, are presented in this paper. The mortars containing alkali activated slag show very high heavy metals immobilization ratio. Probably it is an effect of phase composition of the mortars and absence of capillary pores in their structure.

The properties of mortar and concrete using the mineral admixture consisting of red mud and finely ground silica were investigated in order to use effectively an industrial byproduct from a chemical factory. This paper reports on the effects of five mixing ratios of red mud to finely ground silica on flow value and air content of fresh mortar, compressive strength, resistance to chloride penetration, and sulfate resistance of hardened mortar compared with those of plain mortar. Secondly, the compressive strength and the drying shrinkage of concrete specimens cured at 20 C in water and a steam chamber at the maximum temperature of 65 C were investigated on the concrete using the admixture consisting of five percent red mud and five percent finely ground silica and 10 percent finely ground silica only. The substitution was 10 percent of cement. The flow value of mortars tends to decrease with an increasing rate of red mud content, when the substitution of the mineral admixture for cement is 50 percent. The air content of fresh mortar becomes maximum when the mixing ratio of red mud and finely ground silica is equal. The compressive strengths of mortars containing red mud are lower than that of plain mortar at each age. The mortars containing finely ground silica exhibit higher strength from seven to 28 days. The resistance to chloride penetration and the sulfate resistance of the mortars are clearly improved by the use of this mineral admixture. The compressive strength of concrete at each age using red mud as a single admixture increases slightly when compared to concrete using the admixture consisting of red mud and finely ground silica. The drying shrinkage of the concrete using this admixture is higher than that of plain concrete, and the shrinkage is slightly reduced by the adoption of steam curing.