Properties of self-compacting concrete containing granite dust particles

In the course of production in the Granite Industry, a lot of quarry dust wastes is generated which is either heaped at sites causing environmental and health hazards or dumped in landfills causing ecological problems. It is imperative to evolve a viable option for disposal so to rid the environment of this menace. This study investigated the use of quarry dust particles (QDP) generated from the granite industry as a cement replacement in self-compacting concrete (SCC). The experimental program was carried out in two phases: the first phase optimized the amount of QDP as replacement of Portland cement (PC) with acceptable flow-ability. The second phase evaluated the fresh and hardened properties of SCC which include tests on slump flow, J-ring and L-box to determine filling, passing abilities of SCC while compression and splitting tensile tests were conducted to determine the compressive and splitting tensile strengths, respectively. Test results show that at 20% replacement of cement with QDP, the SCC-QDP mixes has a slump ranged from 642 to 730 mm compared with 578 mm for SCC mix, a compressive strength of 37 N/mm2 compared with 30 N/mm2 for SCC. This was enhanced by QDP which filled the voids between the coarse grains of cement and water molecules which facilitated the flow ability of the mixes and then at later ages reacted with liberated calcium hydroxide from cement hydration to enhance the strength of the mixes. The results then indicated that QDP can be used to replace PC up to 20% by mass of PC in the production of SCC without adverse effect on both fresh and hardened properties. This results also show that QDP, a suitable material for partial replacement of PC in SCC production, can be used to reduce demand for cement thus reducing carbon dioxide emission and also solve other environmental problems

Hydration Behaviour and Characteristics of Binary Blended Metakaolin Cement Pastes

Cement production consume large amount of energy to form clinker and carbon dioxide (CO2) emitted into the atmosphere causing global warming. To mitigate this challenge, the use of Metakaolin (MK) as supplementary cementitious material cannot be over emphasized. This study evaluated the use of Metakaolin (MK) on hydration development of MK--PC blended cements and strength of Mortars. The MK with a Blaine fineness of 7883 cm2/g was used to replace Portland Cement (PC) at a level of 0, 5, 10, 15, 20, 25 and 30 % by mass of PC at a constant w/b ratio of 0.50 to prepare blended cements. Hydration development of blended cement and compressive strength of Mortars were investigated using chemically bond water and free-lime contents and strength tests respectively. X – Ray diffraction (XRD) and scanning electron Microscopy (SEM) techniques were also utilised in the analysis of Pozzolanic reaction and hydration products. Test results indicates that Water of consistency, setting times for the mixes increased with increase in MK contents, influence of MK on the chemically bond water and free Lime contents of the blended cements were due to its filler and dilution effects and Pozzolanic reaction. The cumulative non-evaporable water and free-lime contents increased by partial replacement of PC with MK due to PC hydration and Pozzolanic reaction. The tested Mortar prepared with blended cements with 30 % PC replacement with MK shows a retardation of strength development with a low value at early ages (7 days) and increased in growth at later ages (28 days). The compressive strength of tested mortar for 90 days curing age for the blended mortar is 31 N/mm2 close to that of control Mortar (35 N/mm2). The results obtained from XRD and SEM analysis indicated increase in Calcium Hydroxide (CH) consumption and Calcium Silicate hydrate (C-S-H) formation in blended cement pastes with curing time. The PC replacement with MK induced changes in Microstructures of blended cement paste and chemical composition of hydration products. These results are potentials for modelling the behaviour of MK-PC blended cements

Properties of steel fiber self-compacting concrete incorporating quarry dust fine powder

Self-compacting concrete (SCC) has great potentials as it offers several environmental, economic and technical benefits. Moreover, the use of fibers extends its possibilities since fibers arrest cracks and retard their propagation. Incorporation of Quarry Dust (QD) in SCC help to reduce environmental hazards during the production of QD. This study evaluated the fresh and hardened properties of steel fiber self-compacting concrete (SFSCC) incorporating QD. The optimum fiber and QD contents with no adverse effects on fresh and hardened properties were determined. A comparative study on behavior of SCC and SFSCC mixtures in terms of workability, compressive strength, compressive strength development ratio, tensile, flexural and energy absorption capacity was carried out. Test results showed that compressive strength increased with increase in QD contents at fixed fiber content by mass of Portland cement (PC) and then decreased. Strength development ratio (C28/C7) for SCC was 1.13, while it was 1.06, 1.08, 1.10 and 1.01 after reinforcing with 0.10, 0.20 and 0.30 contents of fiber. The compressive, tensile, flexural and energy absorption capacity or Toughness of SFSCC increased with the inclusion of the aforementioned contents of steel fiber up to 0.20 % volume of total binder at constant QD content and then decreased when compared with control SCC values. From these results, optimum value for the variables studied was obtained from mix QD20 + 0.2fr. Hence, steel fiber and QD could be successfully used in SCC production not minding the slight draw back on workability of SCC caused by inclusion of steel fiber, but with a modified dosage of super-plasticizer (SP), fresh and hardened properties, in accordance with specifications in relevant code(s) can be achieved

Evaluation of Ductility Index of a Rectangular Beam Reinforced with Rebars Milled from Scrap Metal

Ductility index is essential both in structures and structural elements in service. Its inadequacy may lead to brittle failure and jeopardize the lives of occupants. In reinforced concrete beams that experience large inelastic deformation in service, its ductility index cannot be over- emphasized. In Nigeria, the steel sector is now sustained through the recycling of scrap metal obtained mainly from municipal solid wastes which find application in the construction Industry. The study evaluated the ductility index of a rectangular concrete beam reinforced with rebars milled from scrap metal. This was achieved by designing the beam, produced samples and assessed its behavior under load experimentally and analytically with emphasis on the deflection ductility index. Eighteen (100 mm x 200 mm x 1000 mm) concrete beams reinforced with rebars milled from scrap metal were produced; six each with concrete strength of 20.33, 26, 30 N/mm2 and steel ratio (ρ) of 0.0058 to 0.012 respectively. The samples were tested under a four- point loading and analyzed using the Hognestad models for concrete and steel, theoretical equations of strain compatibility and equilibrium of forces at the beam section. Based on the test data obtained in the laboratory and analytical approach, the failure mode of most beams was classified as ductile flexural failure accompanied by yielding of the tension steel preceding the crushing of concrete. The flexural capacity of the test samples ranged from 43.25 to 88.25 Kn with a deflection ductility index of 1.72 to 2.80. The analytical load-deflection relationship compared with experimental values show good agreement. This confirms the applicability of the theoretical approach which provides a useful tool for evaluating the deflection ductility index and load-deflection response of concrete rectangular beams reinforced with rebars milled from scrap metal. Key words: Ductility index, concrete beams, Rebars, scrap metal, deflection response