Workability is one of the factors that affect concrete strength and durability in addition to the cost of labor and the appearance of the final product. It is a vital feature of the concrete that must be measured properly to ensure the quality of concrete. This paper presents a method for predicting equations for workability of concrete and correlation between the workability tests by using Pearson correlation coefficient. The results show that the developed model is accurate and it can be used for prediction of the workability parameters with a high degree of accuracy. Based on statistical analysis, the correlation was significant at the 0.01 level (2-tailed) between the workability of concrete tests. Regression equation relating compacting factor and slump was based on nonlinear general equations (C= 0.5371S^0.1204) and also nonlinear equations were found between Vebe and slump tests (V = 8.0689e−0.0175x).
The main aim of this investigation is to study the combined effect of hot-dry weather conditions on the plastic and drying shrinkage of high performance lightweight aggregate concrete (HPLWAC) specimens, along with the other properties including, workability, setting time compressive and splitting strength. The experimental program including the use of fixed mix proportions and was carried out in a typical Iraqi summer day (under actual conditions) of different times during the day. The results indicate that the use of lightweight aggregate play a main role in decreasing the effect of hot dry weather on plastic shrinkage, as well as the plastic shrinkage strain of HPLWC specimens cast at 12:00 pm. less than that of normal weight aggregate concrete specimens by about 36.7%. While drying shrinkage of HPLWC specimens at initial ages up to 7 days was low and it increases with a higher rate at later ages.
The aim of this investigation is to produce high performance lightweight aggregate concrete in actual hot-dry weather conditions, and then study the combined effect of hot-dry weather conditions on the fresh properties of high performance lightweight aggregate concrete such as workability, initial and final setting time, measuring concrete temperature, and hardened concrete properties (compressive strength, splitting tensile strength and flexural strength, modulus of elasticity). The experimental program including the use of fixed mix proportions and was carried out in a typical Iraqi summer days (under actual conditions) of different times during the day, where the mean maximum temperature in shadow in July and August usually is more than 44° C and relative humidity of about 24 %, the results were compared with the specimens prepared and casted in laboratory and others in shadow site. The results indicate that as temperature rises, and relative humidity falls, the initial and final setting time were reduced, beside that actual drop in slump. The results also show that rising placing temperatures more than allowable concrete temperature that recommended in ACI 305 does not, as a rule, lead to lower strengths. The strength performance of concrete can remain unaffected by higher placing temperatures, or it can even improve over that at lower temperatures. Using pre-soaked lightweight aggregates (pumice) as internal water reservoirs for producing this type of concrete under actual hot-dry weather condition played positive role in improvement of concrete properties by compensate the evaporation of water due to the rising temperature and decreasing relative humidity, and provide additional moisture in concrete for a more effective hydration of the cement.
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