Effect Of Delayed Casting Of Concrete-On-Concrete Strengh Due To Formation Of Cold Joint

Abstract

Delayed casting of concrete forms a joint between hardened and newly placed fresh concrete which is commonly called construction or cold joints and affects strength of concrete. An experimental investigation was performed to evaluate the effect of different delayed casting of concrete on strength of concrete due to cold joint formation and configuration. A total of 44 number of concrete specimens were produced, out of those 12 numbers of (150*150*150mm3 ) cubes were used to determine the compressive strength, 12 number of (Ф=150mm and h=300mm) cylinders were used to determine the split tensile strength and 20 number of (100*100*500mm3 ) beam specimens were used to determine flexural strength of concrete with different cold joint formation time and configuration at the end of curing period of 28 days. For all samples firstly fresh concrete specimen was produced by placing fresh concrete for half cylinder, cube, or beam mold and for the remaining half filling of the cylinder, cube or beam mold freshly mix concrete was casted with the times laps of 0, 7, 14, and 21 days and metallic molds was used to produce vertical, horizontal, and inclined cold joint configuration in each separation; therefore, the resulting plane was flat. Finally, the ultimate strength tests were recorded and analyzed on each of these samples at the ages of 28 days of curing time to study the behavior for the joints under compressive, split tensile and flexural strength of concrete. From laboratory test result it was observed that percentage reduction of compressive strength of concrete when casting the second layer of cube specimens after 7, 14 and 21days where 5.92%, 14.07%, and 28.54% respectively with respect to reference specimens. The reduction of tensile strength of concrete when casting the second layer of cylinder specimen after 7, 14 and 21 days where 10.75%, 12.9%, 32.25% respectively compared to control specimen. Flexural strength was decreased with increasing times delay of casting the second layer of concrete with inclined, horizontal, and vertical failure plane of beam specimens where 32.38%, 22.86% and 52.85% respectively. From laboratory test result it was observed reduction of concrete strength was increased when delay period of casting increases.