International Concrete Abstracts Portal

Several superplasticizers were synthesised by an esterification reaction using commercial polymethacrylic acid and polyethylene oxide chains to produce comb-type polymers. These superplasticizers, with same main chain length, but different ester ratios were evaluated in self-compacting concrete (SCC) using cement with a high C3A and soluble alkali content. There is a strong relationship between the initial efficiency (flow value) and the carboxylic ester ratio of the polymeric material. In order to further understand this relationship, preliminary adsorption isotherms using a basic calcium carbonate suspension medium in the presence of these polymers, with and without an addition of sodium sulphate were investigated. The results show clearly that the level of adsorption in a basic calcium carbonate suspension medium decreases when the concentration of sodium sulphate increases, and strongly decreases when the comb-type polymers ester ratio increases. The results tend to show an effect of ionic strength and not an effect of ions influence.

An equation was formulated for estimating the plastic viscosity of cement paste containing an air-entraining admixture, which is a commonly used chemical admixture for concrete. Air-entraining admixtures slightly increase the plastic viscosity of neat cement paste. The viscosity equation was derived by incorporating this effect, to minimize the difference between the estimation and measurement. The ratio of the plastic viscosity estimated from the proposed viscosity equation to the measured plastic viscosity was found to be approximately 1, the anticipated value. Viscosity equations for mortar and concrete also formulated based on an existing viscosity equation were found to be valid even when the plastic viscosity of the matrix changed.

Concrete that is to be placed under cold weather conditions must be protected from freezing and may be required to have adequate setting behavior and strength development. There are a number of different approaches that can be used to ensure protection from freezing and the development of mechanical properties of such concrete. One approach is the addition of chemical admixtures that accelerate the cement hydration in the concrete. This paper presents the results of studies that examined the performance of a new cold weather admixture (CWA). The performance of the CWA was evaluated in concrete with an initial concrete temperature of 11-13°C that was cured at an air temperature of either -1 °C, -7°C, or -11 °C. The addition of the CWA allowed the concrete to set and gain strength under the cold weather conditions. Lowering the w/c of the concrete with a high-range water reducing admixture coupled with the addition of the CWA further improved the setting and strength development of the concrete at the lowest curing temperature tested. These results suggest that the use of the CWA will allow current cold weather concreting guidelines to be revised to allow for lower initial concrete temperatures.

The effects of calcium nitrite based corrosion inhibitor (CNI) and fly ash on the corrosion of high performance concrete subjected to a simulated marine environment were investigated. Small-scale concrete slabs containing steel reinforcement were cast with a cover depth of 20 mm and with a construction joint intersecting the steel reinforcing at right angles. The slabs were subjected to a simulated marine environment with two cycles of wetting and drying per day. Corrosion activity of the reinforcing bars was evaluated using the linear polarization resistance technique and free water-soluble chloride content at the rebar level was determined at the end of the testing period. Testing in areas away from the construction joint and away from corrosion induced cracking revealed that the water to cementitious materials ratio (w/cm) has a significant effect on the ingress of chlorides. Thus, chloride content obtained for 0.29 and 0.37 w/c were less than one third that of 0.45w/c concrete. Furthermore, a reduction in the amount of chlorides at the rebar level was clearly demonstrated when fly ash was used in 0.45w/c concrete.

The paper summarizes the results on flowing and cohesive superplasticized mixtures studied and placed in the 1970's and 1980's with properties very close to those of Self-Compacting Concretes (SCCs) presently considered to be the most advanced cementitious material. Case histories (from Hong Kong, New York, and Trieste, Italy) concerning placing of superplasticized self-levelling concrete without any vibration at all, published in the 1980's, are re-examined to compare them with the present SCCs. In particular, the paper deals with the ingredients of these mixtures (superplasticizer, cement, fly ash, ground limestone, silica fume, etc.) by examining their specific role in determining the main properties of these concretes, such as fluidity, on the one hand, and resistance to segregation, on the other. Some interesting new materials, such as ground fly ash or powder from recycled aggregates, appear to be very promising for manufacturing SCC in agreement with the requirements needed for sustainable progress.