International Journal of Scientific Engineering and Research (IJSER) ISSN (Online): 2347-3878 Impact Factor (2018): 5.426 Volume 8 Issue 1, January 2020 www.ijser.in Licensed Under Creative Commons Attribution CC BY Cracking Behavior of Base Restrained High Strength Plain Concrete Walls Due to Shrinkage Ali A. Al-Tameemi 1 , Ali N. Attiyah 2 , Tasneem J. Mohammed 3 1 Assit. Prof. of Properties and Strength of Materials, Department of Civil Engineering, Faculty of Engineering, Kufa University, Kufa- Annajaf Road, Annajaf, Iraq aliam.altameemi [at]uokufa.edu.iq 2 Assist. Prof of Structural Engineering, Department of Civil Engineering, Faculty of Engineering, Kufa University, Kufa-Annajaf Road, Annajaf, Iraq alin.diebil [at]uokufa.edu.iq 3 Post Graduate Student at Faculty of Engineering, Kufa University, Kufa-Annajaf Road, Annajaf, Iraq tj261933 [at]gmail.com Abstract: The cracking caused by volume change in plain and reinforced concrete walls restrained at their bases is a widespread problem. Moreover, when High Strength Concrete (HSC) may be used in construction of such walls, cracking behavior of such walls due to shrinkage must be studied. In this work, six walls with Length/Height (L/H) ratio of 6, 8 and 12, were cast using high strength concrete and monitored for 90days after appropriate curing. All the walls were of 500mm height and 100mm thickness and without horizontal reinforcement but only 150mm length vertical dowels extended from the base to provide base restraining. In the present work four out of six walls had been cracked, this finding is in conflict with what was believed by many researchers that base restrained high strength concrete walls could not cracked under weathering conditions. ACI 207.2R stated that cracks under shrinkage effect cannot be eliminated, but it was shown in this work that cracking could be prohibited by limiting the L/H ratio to be 6 or less in base restrained high strength plain concrete walls. In the current work it was shown that there were a large difference between the observed values of maximum crack width, minimum and maximum crack spacing in high strength base restrained concrete walls and those values calculated utilizing the equations developed for normal strength base restrained concrete walls. Keywords: High strength concrete, Shrinkage, base restrained walls 1. Introduction High Strength Concrete (HSC) is commonly defines the concrete having a 28days compressive strength more than 60 MPa [1]. HSC has been advantageously used for many structural members like columns and shear walls of multistory buildings. Such concrete is being specified where reduced weight is important or where architectural considerations require slenderer vertical load carrying elements [2]. The cracking caused by volume change in concrete walls restrained at their base is a widespread problem. Concrete shrinks when it is exposed to a drying environment causing loss of pore water. Based on that the following classification on the types of shrinkage can be made; plastic shrinkage, autogenous shrinkage and drying shrinkage. The amount of shrinkage depends on many factors: a-Type of cement, Troxel [3] concluded that shrinkage of low heat cement (type IV) is greater than that of (type I). This is believed to be due to high (C2S) content in (type IV) cement, which exhibits high shrinkage. b-Coarse aggregate as concrete, with higher aggregate content and higher modulus of elasticity exhibits smaller shrinkage. Moreover, aggregate with rougher surfaces is more resistant to the shrinkage process. c- Curing duration, Powers [4] reported that prolonged moist curing delays the initiation of shrinkage but the curing effect on the shrinkage magnitude is small. d- Water content, Carlson [5] reported that a decrease of water content of concrete by 15 percent causes a decrease in shrinkage of about 30 percent. e- Temperature and Relative humidity, a high temperature and a low relative humidity of the ambient environment accelerate the diffusion of the adsorbed water and capillary water so as to increase shrinkage [6]. f- Admixtures, also affect the amount of shrinkage but their effect varies from admixture to another [12]. 1.1 Shrinkage Induced Cracking Concrete is always under some degree of restraint, either internally or externally. Internal restraint is a result of steel reinforcement imbedded in concrete and the rigidity of the aggregate, while external restraining is due to the connection with the foundation or other part of the structure. The exposure to environment conditions like temperature and humidity leads to contraction in concrete, consequently the restraining will resist that contraction. So, tensile stresses will develop within the concrete. These stresses increase with time with a decreasing rate due to decreased shrinkage and due to stresses relaxation in concrete. Relaxation occurs and may prevent the development of cracking when the shrinkage develops slowly. Cracking will occur when the tensile stress that is caused by the restrained shrinkage (reduced by relaxation) exceeds the tensile strength of concrete [7]. 1.2 Tensile Strain capacity Tensile Strain capacity is defined as the maximum strain that concrete can endure in tension before cracking occurs. Tensile strain capacity is affected by some factors like moisture content, mix richness, amount and type of aggregate and age of concrete. The effect of concrete age on tensile strain capacity is a confliction point between researchers as some researchers found that tensile strain capacity increased Paper ID: 18012001 DOI: 10.21275/18012001 5 of 10