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

Du PLessis, Louise (2015-12)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: 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.

AFRIKAANSE OPSOMMING: Grond ondersteunde vloere is die mees gewilde tipe vloer vir die grondvloer van strukture sonder kelders. Hierdie vloere word van beton gemaak wat 'n bekende konstruksie materiaal is. Beton het die kapasiteit om ‘n relatiewe hoë drukspanning te kan weerstaan, maar as gevolg van beton se relatiewe lae trekspanning, kraak die beton maklik onder as dit bloodgestel word aan trek kragte. Krake in die beton vloere wat deur laagwerk en direk deur die grond ondersteun word, verminder die diensbaarheid en duursaamheid van die vloer. Die gebruik van sintetiese vesel gewapende beton in grond ondersteunde vloere, het bewys dat dit groot voordele het veral in die beheer oor die aantal en die grootte van krake wat vorm as gevolg van droog krimping. 'n Ondersoek is gedoen om die effek van plaaslik vervaardigde makro-sintetiese vesels op die droog krimping krake in grond ondersteunde vloere te bepaal. Dit word gedoen deur gebruik te maak van ‘n groot-skaalse toets wat die droog krimpings krake van polipropileen vesel gewapende beton (PPFRC) te vergelyk met dié van konvensionele beton. Die resultate van die groot-skaalse toetse word dan vergelyk met dié van 'n eindige element metode (EEM) model. Die verskillende materiaal eienskappe van die PPFRC wat nodig is vir die EEM ontledings, word verkry deur drie-punt balk buigtoetse, wig splyttoetse, druktoetse en materiaal krimping toetse. Die effek van die vesels word getoets in terme van die verskillende spasiërings tussen die gesnyde voeë, die verskillende vesel volumes, die blad dikte en die graad van wrywing tussen die beton en die sub-basis onder die beton. Daar is gevind dat die gebruik van makrosintetiese vesels lei tot 'n toename in die getal krake tussen die gesnyde voeë. Alhoewel daar 'n toename in die aantal krake is, dra die vesels in die beton by tot ‘n afname in die kraak wydtes. Die gebruik van SynFRC in grond geondersteunde vloere sal dus lei tot 'n toename in die aantal krake, maar met kleiner kraak wydtes, soos die spasiërings tussen die gesnyde voeë toeneem.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97777
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