عنوان مقاله [English]
From a strength point of view, lightweight concretes are categorized into three groups of structural, semi-structural and non-structural concretes. The main purpose of this research is to determine the optimum mix design of a semi-structural lightweight concrete composed of pumice aggregates with the lowest unit weight and a reasonable compressive strength. For this purpose, the Taguchi method, with four effective factors and three levels, has been adopted. The method is a systematic design of experiments which can efficiently reduce the time and cost of experiments. In this method, the most effective factors are selected and different levels are determined for each factor. Then, based on the number of factors and the assigned levels, a suitable orthogonal array is chosen using the Taguchi guideline. These arrays can provide a regular program for the experiments, including the number of tests and the combination of different levels in each test. At the end of each test, the corresponding quality criterion is obtained. Using the results of systematic tests via MINITAB software, the optimum combination is determined and, thus, the value of the quality criterion under optimum condition is predicted. In order to validate the accomplished study and evaluate the Taguchi method, a proof test, based on the optimum combination, is usually built, and its result is compared with the software prediction. In this research, due to the numerous factors affecting the compressive strength and unit weight of concrete, four governing factors are selected: pumice with sieve type 1, pumice with sieve type 2, sand and filler. In addition, pumice with sieve type 3 has been also selected as a complementary factor. The remaining materials, such as the ratio of water to cement, additives and cement weights, are considered as constant. In order to determine the optimum combination, the orthogonal array of L9 is utilized and after the analysis and determination of optimum levels, the results of laboratory proof tests and prediction of the Taguchi method were compared. The results demonstrate that the systematic Taguchi design method is very useful in reaching the optimum mix design of semi-structural lightweight concretes.