Heat of hydration of cement and resulting thermal gradient has a great influence on the quality of concrete and concrete structures particularly in the mass concrete for dams. In roller compacted concrete (RCC) method for dam construction, surface of concrete layers are very large in comparison with thickness of the layers. Therefore the thermal condition in the center of layers is almost adiabatic in horizontal direction. t means that, the generated heat of hydration mostly flows in the vertical direction and a great proportion of heat dissipates through the upper face of the layer before the next layer is placed. Low thermal conductivity of concrete layers has a great influence on the dissipation of generated heat. Thermal gradient induced by generated and remaining heat in the layers can cause thermal cracking in RCC dams which have no post-cooling system. In this investigation a laboratory model is set up to optimize the layer thickness and required time for dissipating of generated heat and controlling thermal cracking. The laboratory model consists of a 90x90 cm cylinder filled with 3 layers of concrete with 30cm thickness each layer. In this simulation the variables were the thickness of layers and the exposure time for each before placing the subsequent layer. Temperature variations were recorded at the center of each layer and at different distances from the center of the laboratory model. From the results of this research, the thickness of the layers and their related exposure time were determined for various concrete mixtures in order to minimize the heat problem and thermal crack prevention. The proposed guide for placing concrete in RCC dams seems to be beneficial for the construction of such dams under various conditions.

A series of roller-compacted concretemixtures were developed for the Norwegian Skjerka hydropower project. The mixture optimization was based on the medium-paste concept of the International Committee On Large Dams (ICOLD) using crushed aggregate from the dam site. The mixture optimization consists of a two-step procedure minimizing the paste content, keeping the compacted density above 97.5 % of the theoretical air-free density, and giving an optimal loaded Vebe time of 10 - 20 seconds. Nine mixtures were produced using low calcium fly ash and portland cement with various fly ash-cement propotions. The water-binder ratio was kept constant at 0.53 according to the Norwegian code for mass concrete for dams. The laboratory test results showed that 8 of 9 binder combinations produced RCC within the design criteria. The compressive strength development of the water-cured specimens was impressive despite the rather low cement contents, giving 1 year strengths of 2 times the 28-day strengths. The use of high-volume fly ash concrete for RCC dams is one example of concrete in harmony with lower environmental impact and less use of resources.

The potential use of Malaysian fly ash cement in concrete has been studied in terms of its influence on elastic properties, volume stability and durability properties. In durability studies, the resistance to chloride ingress, sulfate attack, and suppression of alkali-aggregate reactivity were examined. The results are presented and discussed. The role of the fly ash on heat of hydration, production of roller-compacted concrete, and high-strength, high-performance concrete have been proven in practice. Understanding the influence of fly ash on both fresh and hardened properties of concrete has led to its appropriate use in many important structures in Malaysia. They include the Petronas Twin Towers, the second Malaysia Singapore Causeway, and more recently considered for the construction of a major RCC dam. Properties of fly ash concrete are discussed with examples of application.

Roller-compacted concrete (RCC), because of its superior properties, Synopsis: low cost, rapid and relatively simple construction methods, and proved performance, has been used extensively in recent years in rehabilitation projects at existing concrete and earth and rockfill embankment dams and related hydraulic structures. These applications include increasing the existing spillway capacities, construction of new service and emergency spillways, overtopping protection, and seismic strengthening. This paper presents case histories of selected applications of RCC in rehabilitation of dams and related hydraulic structures. These case histories are presented to show the range of previous applications and to illustrate typical design and construction practices in repair and rehabilitation of dams with RCC. For each of the case histories presented in this paper, an attempt is made to discuss (a) the description of the project, (b) the cause and extent of the deficiency that necessitated rehabilitation, (c) design details, (d) RCC mixture proportions, (e) description of materials, equipment, and placement procedures, (f) cost, and (g) RCC performance to date.

This paper explains the development of a roller-compacted concrete for constructing or renovating concrete pavement (RCCP), using lignite fly ash in Thailand. A method for proportioning the lignite fly ash RCCP based on the ratio, y, between paste volume and void content of total aggregate is proposed. It was found from the tests conducted by varying fly ash replacement ratio, water to total binder ratio, and paste content that the range of value of y which gives rise to optimum strength and density of the RCCP were in between 1.02 and 1.05 for the tested materials. The design curves for compressive strength were derived based on test results with varied fly ash replacement ratio and water to total binder ratio of the RCCP with y being equal to 1.02. Some selected RCCP mixtures were compared with conventional concrete for constructing pavement in terms of flexural strength, drying shrinkage and abrasion resistance. The tested RCCP specimens were found to have higher flexural strength than the ACI-proposed formula for conventional concrete. Drying shrinkage of RCCP was smaller than that of the conventional concrete and was even smaller when lignite fly ash replacement ratios were larger. Similar to the conventional concrete, the abrasion resistance of the RCCP was found to have a good correlation with compressive strength.