Rheological and Structural Properties of Foamed Laterized Concrete
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Foamed concrete is a lightweight material with self-compacting rheological properties. Conventionally, it is produced from mixture of cement, fine aggregates (dredged sand) and mechanically entrained foam. Research findings have shown that the foam degenerates to create evenly distributed macro and micro air pores after 45 minutes; also, that other fine aggregates could be used as partial replacement of the dredged sand. In this respect, it has been established that laterite which is usually available near project sites and less expensive to procure is suitable as partial replacement of dredged sand in concrete. The particle size distribution of dredged sand contains inter-particle voids that contribute to the formation of macro air pores. These macro pores are defects that reduce structural properties of foamed concrete. In addition, non-application of foamed concrete made with available local materials in developing countries is due to dearth of information on its structural properties and the structural strengths of elements made with it. Thus, the application of laterite as partial replacement of dredged sand in foamed concrete to reduce macro pores with minimal impact on the rheological properties was examined. This study consists of two parts namely, preliminary and main investigations. During the preliminary investigation, the effects of replacing dredged sand with laterite on the rheological property (measured as spread diameter) and compressive strength of cube specimens at 28th day were examined. The variables were curing periods, methods of curing and proportions of laterite (0-100 % replacement of dredged sand by weight at interval of 10 %). In the main experiment, the structural properties of foamed concrete made with laterite between 0 and 25 % and the strengths of reinforced concrete beams made with the specimens were examined. Also, three curing methods namely; air, water, and initial curing in water for seven days before exposure to air curing for the remaining curing days were used. The results obtained at the preliminary stage showed that foamed concrete samples with laterite between 0 and 25 % as partial replacement of dredged sand satisfied flow consistency requirement and self-compacting rheological criterion: the spread diameters obtained which are between 532 mm and 642 mm are according to established specifications. The compressive strength of foamed concrete at 28th day increased with increases in proportions of laterite for specimens cured in all curing media. These results formed the basis for the main investigation using laterite in the proportions of 0, 5, 10, 15, 20 and 25 %. The results obtained from the main investigation, showed that specimens made with 25 % laterite content and cured initially in water for seven days before exposure to air curing developed the maximum 28th day structural properties: compressive strength (17.2 N/mm2), split tensile strength (2.38 N/mm2) and modulus of rupture (3.72 N/mm2). These structural properties are greater than the minimum values recommended in ACI 213R (2014) for structural lightweight concrete. Therefore, the foamed laterized concrete with laterite as partial replacement of dredged sand between 0% and 25% in this investigation fit properly into the range of specifications for lightweight structural concrete and thus has the potential of application in such areas as load bearing walls, short span beams and slabs, low volume drain and infill in ribbed floor system. The differences in cost benefit analysis between 0% foamed laterized concrete and specimens with 5, 10, 15, 20 and 25 % laterite were 1.75, 3.5 110, 111 and 113 % respectively. These values justify the application of laterite as partial replacement of sand in foamed concrete production but with an optimum value of 25 % partial replacement of dredged sand with laterite.
University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation
Foamed concrete , Structural properties , Dredged sand , Rheological properties.
Ukponu, B.E (2016) Rheological and Structural Properties of Foamed Laterized Concrete. University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation.