Prof. Gamal Elsayed Abdelaziz :: Publications:

Schmidt Hammer (SH) test is a well-known non-destructive in-situ testing technique for evaluating uniformity and compressive strength of existing concrete structures. The ability of SH to accurately assess strength and variability of concrete was the subject of several research investigations. Majority of these researches does not recommend the use of SH to predict concrete strength while they accept it to assess concrete variability. In spite of that, no real analytical or experimental work was carried out to assure the reliability of SH testing technique in evaluating such concrete variability. The main objective of this paper is to investigate the ability of SH testing technique to accurately measure the concrete variability using different statistical approaches, namely traditional and t-Test. The significance difference between the average means of SH rebound numbers (RN) readings for two sets of concretes are firstly studied, one with equal standard cube strength, while the other is having unequal strength. This was then followed by evaluating concrete variability for various concrete samples taken from different projects by evaluating the coefficient of variations for both standard cube strength and RN results. The within member effect on SH readings are also investigated for different structural elements, namely slabs, columns and shear walls. The research results showed that variability of concrete strength can be significantly assessed by using SH measurements. In addition, a good correlation has been established between the coefficient of variation of RN values and that of cube strength. The results also indicated that Schmidt hammer readings are influenced by the relative location of measurement within the concrete column.