The effect of macro-synthetic fibres on the drying shrinkage cracking behaviour of concrete slabs on grade

Slabs on grade are the most commonly used floors for the ground floor of structures without basements. These slabs are made from the generally used construction material called concrete. Concrete is known for its relatively high compressive strength, but because of its comparatively low tensile capacity the concrete cracks easily under tensile forces. Cracks in the concrete slabs on grade reduce the serviceability and durability of the floor. The use of synthetic fibre reinforced concrete (SynFRC) in slabs on grade has shown major advantages particularly in controlling the extent and size of cracks that are formed due to drying shrinkage. An investigation is done to determine the effect of locally produced macro-synthetic fibres on the drying shrinkage cracks in slabs on grade. This is done thought a large scale test that compared the drying shrinkage cracking of polypropylene fibre reinforced concrete (PPFRC) with that of conventional concrete. The results of the large scale tests are then compared with that of a mathematical finite element method (FEM) model created in a finite element program called Diana. The different material properties of the PPFRC that are needed for the FEM analyses are obtained through flexural three point beam tests, wedge splitting tests, compression tests and shrinkage tests. The effect of the fibres are tested in terms of the different spacings between saw cut joint, the different fibre dosages, the slab thickness and the degree of friction between the concrete and the sub-base under the concrete. It is found that the use of macro-synthetic fibres results in an increase in the number of cracks between the saw cut joints, especially if the joint spacing is increased. Although there is an increase in the number of cracks, the use of fibres does consequently lead to a decrease in the crack widths. The use of macro polypropylene fibres in slabs on grade will thus result in an increase in the number of cracks, but with smaller crack widths, especially with an increase in spacings between the joints.National Research Foundatio