Experimental Investigations on Temperature Gradient in Massive Raft Foundation

Thermal cracks are the major problem as temperature increases in massive concrete structures. It is imperative to investigate the temperature rise and to find effective techniques to control the heat of hydration of massive concrete. In this research, based on a segmental model test of high rise building raft, the temperature field for the bottom, middle and top surface concrete of the raft caused by the heat of hydration were measured. Blast furnace slag cement (CEM III/A 42.5N) was used due to its lower percentage of C3A and C3S and lower surface area. The tested temperature rise curves indicated that the temperature increases quickly but diminishes gradually. The maximum temperature rise at the middle surface of the concrete reached 56oC, and the maximum temperature difference between the middle and the top surface was 15.80oC. The most extreme temperature difference between the top surface and the surrounding environmental temperature was 26.5oC. So, using slag cement controlled the heat of hydration of concrete leading to environmentally friendly concrete mixes

Analysis of sulfate resistance in concrete based on artificial neural networks and USBR4908-modeling

One of the available tests that can be used to evaluate concrete sulfate resistance is USBR4908. However, there are deficiencies in this test method. This study focuses on the ANN as an alternative approach to evaluate the sulfate expansion. Three types of cement combined with FA or SF, along with variable W/B were study by USBR4908. ANN model were developed by five input parameters, W/B, cement content, FA or SF, C3A, and exposure duration; output parameter is determined as expansion. Back propagation algorithm was employed for the ANN training; a Tansig function was used as the nonlinear transfer function. It was clear that the ANN models give high prediction accuracy. In addition, The engineer can avoid the use of the borderline 2.5–5% C3A content in severe sulfate environments and borderline 6–8% C3A content in moderate sulfate environments, specially with W/B ratio greater than 0.45

Developing a geopolymer pastes using marble dust

ABSTRACTThis paper investigates the use of marble dust waste, fly ash, and silica fume as raw materials for manufacturing geopolymer pastes. The chemical composition of each raw material is established using chemical analysis (X-ray fluorescence XRF) and mineralogical analysis, X-ray diffraction (XRD) pattern of raw materials. The experimental work was divided into three groups (A, B, C) according to the water to binder ratio (w/b) (A =28%, B = 30%, C = 33%). Each group is further divided into five subgroups according to the percentage of marble dust, fly ash, and silica fume. The samples are cured at 60°C for three days. The properties of the geopolymer pastes are determined by performing the following tests: compressive, tensile, and flexural strength and water absorption. The highest mechanical properties were obtained from mixes containing 70% fly ash and 30% marble dust at w/b = 0.28. It was 40% more than those obtained from control mixes containing 50% fly ash and 50% marble dust. It is worth mentioning that the best amount of marble dust was 30% as the resistance of the geopolymer paste reached values up to 237.8 kg/cm2. The results were confirmed by SEM imaging