ROLLER COMPAQED CONCRETE (RCQ DAMS FOR TROPICAL CONDITIONS

Abstract

Acomprehensive and systematic study on Roller Compacted Concrete (RCC) to be used in dams under tropical conditions has been carried out in this work. The three main objectives of this study are : 1. To develop an appropriate and convenient procedure for RCCmix design. 2. To establish the basic mechanism of development of strength with time for RCC. 3. To carry out a detailed experimental study of the major engineering properties of the RCC required for the design of dams. A simple equation for the Final OptimalRCC Mix Water Content (FORCCMWC) for nonabsorbing aggregates (NAA) of 40 mmmaximum size aggregate (MSA) for RCC mixes has been established by analyzing the results of optimal water content of six RCC Mixes of a previous experimental work (Omran, 1992) which followed ACIC-207 report [2] of preliminary RCC Mix design. [For sizes other than 40 mm MSA, similar equation will come up]. Analysis were made through graphical representation of the results in X- and Y-axis. It relates the cement and fly ash contents of the RCC with the water content that produces the maximum strength. The equation is incorporated in RCC mix design method that has been used for subsequent experimental work in this study. It can be used as a convenient method of RCC mix design instead of the trial and error process for determination of optimal water content recommended in the ACI Committee 207 Report. For RCC mixes with absorbing aggregates, the total water content can be calculated by adding this optimum water content to the water absorbed by the aggregate. The study on strength development of RCC with time has been carried out to observe the effect of curing temperature on the development of strength. Two types of curing were performed in this studv. 0-2 (a) Normal Curing: "Normal Natural Water Curing Outside, NNWCO" the lab was carried out in summer-winter (SW) and winter-summer (WS) sequence. It was observed that the development of strength was slow; i.e., the minimum time required by a specimen for the development of full strength (Almost Peak Cured Strength, APCS) was 550 days. Hot Water Curing: Performed in this work as Single Cycle-Hot Water Curing (SC-HWC) and Repeated Cycle-Hot Water Curing (RC-HWC), both preceded by Normal Curing for several days. Much quicker development of strength was observed in this case compared to the NNWCO; i.e., in RC-HWC (for RCC at hothumid temperature of water at 90°C) the time required by a specimen for the development of APCS was 53 days while the same specimen required 86.8 years at NNWCO for APCS. In RC-HWC (for mortar at hot-humid temperature of water at 103°C) APCS timing was less than 16 days. With rise of hot humid temperature of water in accelerated curing chamber (ACC) from 90°C to 103°C, APCS timing reduces. The study on the major engineering properties for the design of RCC dams consists of the following : , ,,, (a) Split Cylinder Strength: the Split Cylinder tests were performed under various curing conditions and paste mortar ratios. (b) Toughness: Elastic Modulus and Ultimate Modulus determined from RCC cylinder tests under normal and special curing conditions were found to be greater than the values reported by Schrader (1985). (b) 0-3 (c) Joint Strength: A number of tests were performed to establish the ratio of RCC joint strength to material strength from Ultimate Split Tension and Ultimate Split Shear test. (d) Flexural Strength: Two-point loading tests were performed on plain RCC beams under different curing conditions. (e) Drying Shrinkage: Shrinkage tests were performed on plain RCC beams under different curing conditions. Results from specially cured specimens showed Coefficients of Drying Shrinkage between 50-90 micro strains. (f) Bond Strength: A limited number of bond tests for RCC (under different curing conditions) reinforced by steel bars showed that the bonds did not fail until the failure of the reinforcing bars. (g) Thermal Expansion: Coefficient of Thermal Expansion determined for plain RCC beams showed very similar results for different specimens under different curing conditions and temperatures (average value 5.65x10"6/°C). (h) Coefficient of Permeability: Coefficient of Permeability for plain RCC cylinders under curing conditions were found to be quite similar to each other (average value 8.73xl0",2m/sec). 0-