Behaviour of Normal Concrete Us ing Superplasticizer under Different Curing Regimes
The performance of concrete primarily depends upon the type and ratio of its constituents, compaction, curing conditions and admixtures used during curing process. Part of this research emphasis to calculate the consequences on strength of concrete when water-cement ratio is constant and the increase in slump occurs with the increase in amount of superplasticizer by percentage. The rest of the investigation is carried out to study the effects of superplasticizer with different dosages under different curing regimes at an ambient field temperature ranges between 45°C-50°C. For this purpose, a concrete mix at 20MPa with all parameters constant was prepared by using an ASTM C494 type A, and F, anionic melamine polycondensate non-toxic superplasticizer with no chlorides. Different dosages of superplasticizer were used in different batches of all 95 specimens, and cured under different curing conditions and then tested for compressive and tensile strengths following ASTM standards. In all cases, th e water curing up to 28 days testing showed maximum strength. The highest and lowest values of compressive strength were obtained with the addition of 0.5% and 1% superplasticizer respectively. It was found that without increasing the W/C ratio, the addition of superplasticizer exhibits increase in strength.
Evaluation of the Superplasticizer Effect on the Concrete Compressive Strength Using the Tree-Classification Decision Algorithm
Concrete is the most important material in the civil engineering. The concrete compressive strength is a non-linear function of the concrete age and some constituents. These constituents include cement, blast furnace slag, fly ash, superplasticizer, coarse aggregate and fine aggregate. The superplasticizers are among elements which are important in increasing the concrete compressive strength and we are going to analyze here using the tree-classification decision algorithm. The decision trees, usually, are used in classification of a bunch of data. J48 is one of the most favoured ones. The decision trees are developed using information entropy on a collection of training data. J48 is a recursive algorithm that combines the remaining of the following data sets and continues normalizing the output data using the separation process until a uniform classification result obtains. This article evaluates the superplasticizer effect on the concrete compressive strength using the tree-classification decision algorithm.
Effect of High Doses of Chemical Admixtures on the Freeze-Thaw Durability of Portland Cement Concrete
Abstract : The usual approach to increasing concrete's resistance to freeze thaw damage is to modify its microstructure. Because concrete readily absorbs water, when it is in a wet environment and then cooled to below 0, any water that freezes inside the concrete will expand and, depending on the nature of the internal pore structure, could lead to internal micro-cracks. A single freezing event does not cause much harm, but repeated freezing and thawing cause the tiny cracks to grow and ultimately result in conspicuous cracks on the surface of the concrete, known as frost damage. This weakens the concrete and reduces its service life. There are several mechanisms responsible for this damage, so preventing it is complex. However, there are several practical methods used today to counteract problems caused by freezing water, including 1) incorporating entrained air into the concrete to relieve pressures caused by freezing water, 2) using low water-to-cement ratios to minimize the type of voids in which water typically freezes, and 3) using silica fume to refine the pore system so that water may not be able to freeze at normal ambient temperatures. This report reviews the frost damage mechanisms, considers the usefulness of current prevention techniques, and advances a new approach for making concrete resist the deleterious effects of freezing and thawing.