Browsing by Author "Alaud, Salhin Mohamed"

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    Durability of concrete under combined action – mechanical load and alkali-silica reaction
    (Stellenbosch : Stellenbosch University, 2016-12) Alaud, Salhin Mohamed; Van Zijl, GPAG; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: There are still many problems remaining unresolved when concrete structures exposed to combined actions are studied separately, such as, severe environment and mechanical loads. In practice, these conditions act simultaneously, and separate studies may underestimate the rates of deterioration. Alkali-Silica Reaction (ASR) is a major source of deterioration causing cracking in concrete and these cracks may lead to other problems, such as a reduced resistance to the ingress of gas, water and deleterious matter, which in turn have the potential to accelerate the ASR process, but also the carbonation, corrosion and other deterioration processes. An experimental study has been designed to investigate the durability of normal and reinforced concrete elements subjected to the combined action of mechanical loading and degradation due to ASR. Mechanical loading is simulated by the compression, direct tensile, wedge splitting and fatigue (tensile cyclic loads) in pavements due to repeated wheel loads. The environmental action is simulated by means of ASR, induced with the crystalline reaction products. Different mixes with two types of local aggregates, reactive (Greywacke) and non-reactive (Granite) were prepared. Also, ground granulated Corex slag (GGCS) was added to half of the specimens. Reinforced prisms of concrete were prepared to calculate the combined action of mechanical and ASR expansion. Strength and modulus of elasticity under various conditions of ASR were determined from cylinders concrete. Also, wedge splitting on cubes were conducted to monitor the role of ASR on the pre-mechanical cracks. Two methods were followed to determine the ASR effects under combined action; the first was the accelerated method according to the conditions of ASTM C 1260 using a device specially made to immerse specimens in sodium hydroxide solution at 80°C; the second method was carried out over a long period of time (65weeks) according to ASTM C 1293. The specimens in the second method were made with high alkaline and exposed to two conditions, namely partially submerged and high humidity at 38°C. A comparison was made between the behaviour of the specimens exposed to combined action and others exposed to ASR only. Test results indicated that the damage due to combined action is more significant than that due to ASR only. The Granite mixes were less deteriorated than Greywacke mixes. Also the Corex slag decreases this deterioration dramatically. Mechanical cracks were the largest in Greywacke mixes with a higher ASR expansion than the others and the smallest were in Granite mixes with Corex slag. The strength and E-modulus of concrete were reduced due to ASR effects over time. The results from the two methods were different, where the accelerated method (ASTM C 1260) was not an accurate reflection of the ASR of reinforced concrete, but an indicator of the potential deterioration due to ASR. The series method of ASTM C 1293 was more accurate in identifying the changes in mechanical cracks under ASR. Finally, all the results have been reflected in graphs and have been compared and modelled