Wee Tiong Huan
Email Address
cveweeth@nus.edu.sg
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42 results
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Now showing 1 - 10 of 42
Publication Early-age creep and shrinkage of blended cement concrete(2002-01) Li, H.; Wee, T.H.; Wong, S.F.; CIVIL ENGINEERINGThis paper reports a study on the early-age creep and shrinkage of concrete with and without silica fume (SF), ground granulated blast-furnace slag (GGBS), and their combinations. The test parameters were water-binder ratio, aggregate content, partial replacement of cement by SF, GGBS, or both, as well as test conditions (drying versus sealed conditions). The stress-strength ratios at loading were fixed at 30% of the 3-day compressive strength and 20% of the 3-day tensile strength for compressive and tensile creep, respectively. The test environment was controlled at a temperature of 30 ± 2 C and a relative humidity (RH) of 65 ± 5%. The compressive and tensile creep together with drying and autogenous shrinkage were determined over 4 months of loading. The results obtained for plain, double-blended, and triple-blended concrete were assessed and compared to provide guidelines on the use of SF and GGBS in concrete structures subjected to early-age creep and shrinkage.Publication Resistance of blended cement pastes to leaching in distilled water at ambient and higher temperatures(2001-03) Wee, T.H.; Zhu, J.; Chua, H.T.; Wong, S.F.; CIVIL ENGINEERING; BACHELOR OF TECHNOLOGY PROGRAMMEThis paper outlines an investigation on the resistance of ordinary Portland cement (OPC) pastes with and without mineral admixtures to leaching in distilled water at ambient and elevated temperatures of approximately 30 and 80 C, respectively. The effects of water-binder ratio (w/b), mineral admixtures, microstructure, and water-curing period were also explored. An immersion test using thin plate specimens was conducted to accelerate and study the leaching behavior of these materials in distilled water. Mercury intrusion porosimetry was performed to examine the change in microstructure, while thermogravimetric analysis was carried out to determine the free calcium hydroxide and calcium carbonate contents within the cement matrix. Based on visual observation together with change in mass, pore structure, porosity, free calcium hydroxide, and calcium carbonate contents, the resistance of cement pastes to leaching was evaluated, and guidelines on the design of concrete structures subjected to leaching in distilled water at both ambient and higher temperatures are provided.Publication Shear transfer in lightweight concrete(2011-06-01) Emiko, L.; Thamaraikkannan, V.; Huan, W.T.; Thangayah, T.; CIVIL & ENVIRONMENTAL ENGINEERINGThis research studied the shear transfer in lightweight aggregate concrete and foam concrete. Fourteen series of precracked push-off specimens, made with different concrete strengths were tested. The effects of concrete strength and shear reinforcement parameters on shear transfer behaviour, including shear transfer strength, were analysed. Almost all the specimens failed as a result of slippage along the shear plane. Together with experimental results obtained from a literature review, general formulas for shear transfer strength for reinforced lightweight concrete are also proposed.Publication Preparation of high performance foamed concrete from cement, sand and mineral admixtures(2007-06) Pan, Z.; Hiromi, F.; Wee, T.; CIVIL ENGINEERINGThe titled high performance foamed concrete was developed from Portland cement, ultra fine granulated blast-furnace slag, pulverized fly ash and condensed silica fume by means of pre-foaming process. The resultant foamed concrete presents its thermal conductivity of about 0.16-0.75 W/(m • °C) and 28 d compressive strength of about 1.1-23.7 MPa when its mix proportion varies in the range of cement content 280 kg-650 kg/m3, fly ash 42-97 kg/m3, slag 64-146 kg/m3, silica fume 34-78 kg/m3, and sand 0-920 kg/m3. The compressive strength of the foamed concrete with oven dried bulk density of 1500 kg/m3 in appropriate mix proportion and with small amount of superplasticizer reached as high as 44.1 MPa. Meanwhile, the fresh foamed concrete behaves like an excellent flow-ability, therefore, is especially suitable for the application in case of massive foamed concrete casting in situ and in the case of filling casting into large volume underground irregular voids, except for pre-casting of building components like blocks, bricks, and wall panels. © 2007 Wuhan University of Technology and Springer-Verlag Berlin Heidelberg.Publication Effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete(2006-07) Babu, D.S.; Ganesh Babu, K.; Tiong-Huan, W.; CIVIL ENGINEERINGThe aim of this study is to investigate the effect of polystyrene aggregate size on strength and moisture migration characteristics of lightweight concrete. The present study covers the use of expanded polystyrene (EPS) and un-expanded polystyrene (UEPS) beads as lightweight aggregate in concretes that contain fly ash as a supplementary cementitious material. Lightweight concrete with wide range of concrete densities (1000-1900 kg/m3) were studied mainly for compressive strength, split tensile strength, moisture migration and absorption. The results indicate that for comparable aggregate size and concrete density, concrete with UEPS aggregate exhibited 70% higher compressive strength than EPS aggregate. EPS aggregate concrete with small EPS aggregates showed higher compressive strength and the increase in compressive strength was more pronounced in low density concrete when compared with high density concrete. The UEPS aggregate concrete exhibited brittle failure similar to normal weight concrete (NWC), whereas, gradual failure was observed in EPS concrete. Moreover, the moisture migration and absorption results indicate that the EPS concrete containing bigger size and higher volumes of EPS aggregate show higher moisture migration and absorption. © 2006 Elsevier Ltd. All rights reserved.Publication Direct tension test and tensile strain capacity of concrete at early age(2003-12) Swaddiwudhipong, S.; Lu, H.-R.; Wee, T.-H.; CIVIL ENGINEERINGThe tensile strain capacity of concrete under uniaxial tension is investigated using the direct tension test method. The adopted method of testing improves the weak bond strength between the embedded bar and concrete and reduces the stress concentration at the end of the embedded bar. The method has overcome the difficulties in centralizing and aligning the two embedded bars in the specimens. Seven mixes of concrete were designed to study the effects of age, compressive strength and mineral admixture on the tensile strain capacity. The investigation shows that the tensile strain capacity of concrete is a relatively independent parameter. The average tensile strains at failure and at 90% failure load are 120 and 100 μ, respectively. The corresponding characteristic tensile strain values at failure and at 90% failure load are 86 and 78 με, respectively. © 2003 Elsevier Ltd. All rights reserved.Publication Accelerated test of ingress of chloride ions in concrete under pressure and concentration gradients(1996-03) Lee, S.L.; Wong, S.F.; Swaddiwudhipong, S.; Wee, T.H.; Loo, Y.H.; CIVIL ENGINEERINGThis paper describes the experimental and numerical work carried out to study the ingress of chloride ions in concrete under pressure and concentration gradients. The proposed accelerated water and chloride permeability tests together with long-term soaking tests are used to develop a pressure gradient model, a concentration gradient model and the combination of the two for the prediction of ingress of chloride ions in concrete. It is found that the experimental results, based on OPC concrete with a water-cement ratio of 0·6 tested in the pressure range 0-30 MPa, agree well with the finite element solutions derived under similar conditions. The design and application of the specially built testing equipment for the accelerated permeability tests are presented. The repeatability of these tests, expressed as the coefficient of variation, is satisfactory. This confirms that the proposed test apparatus and method can be used with confidence. It is also observed that the applied pressure gradient has little effect on the water permeability coefficient in the experimental range 0-30 MPa.Publication Carbonation of concrete containing mineral admixtures(2003-03) Sulapha, P.; Wong, S.F.; Wee, T.H.; Swaddiwudhipong, S.; CIVIL ENGINEERINGThis study deals with the carbonation of concrete incorporating ground granulated blast-furnace slag (GGBS), fly ash (FA), and silica fume (SF). It is observed that a decreased water-to-binder ratio and replacement level of GGBS, FA, or SF, or an increase in GGBS fineness and curing age in water, led to better carbonation resistance. However, compared to a plain concrete, the concrete incorporating mineral admixtures (except GGBS with higher fineness and SF) generally showed lower resistance to carbonation, possibly due to the dominating effect of the reduction in calcium hydroxide over pore refinement. Hence, adequate curing is recommended for enhancing the resistance of concrete containing GGBS, FA, and SF to carbonation. It is also found that both the carbonation coefficient and compressive strength served as good indicators for the carbonation rate of concrete with and without mineral admixtures.Publication The effect of initial moisture content on water transport in concrete containing a hydrophobic admixture(2002-04) Aldred, J.M.; Swaddiwudhipong, S.; Lee, S.L.; Wee, T.H.; CIVIL ENGINEERINGTests on initially saturated and dried concrete containing a hydrophobic admixture showed that initial moisture content had a significant effect on measured water transport properties. Concrete specimens containing the hydrophobic additive significantly reduced water penetration when the concrete had been initially dried, and had limited or no positive effect on water penetration into initially saturated specimens. The reduction in water transport compared with the control was generally more pronounced in hydrophobic concrete of higher w/c ratio, as well as tender conditions of limited curing and greater drying. The hydrophobic admixture had no significant effect on water vapour diffusivity. These results suggest that the ingredients in the admixture only become effective where a clear wet-dry interface is present and tend to influence water transport through larger pores.Publication Durability of ferrocement - a case study(1996-01) Mansur, M.A.; Paramasivam, P.; Wee, T.H.; Lim, H.B.; CIVIL ENGINEERINGThe results of an investigation conducted on the condition of a 13- year old ferrocement structure which has been left abandoned for the last four years are reported in this paper. A part of the structure has been cut out and appropriate tests were performed to determine the depth of carbonation, extent of chloride-ion penetration, state of the embedded reinforcement and strength characteristics of the composite in tension, compression and flexure. There results and a comparison with those documented at the time of construction indicate that the structure still retains its desired strength. But, due to inadequate maintenance and lack of protective surface coating, it showed some signs of degradation due to corrosion of the embedded reinforcement. Measures are suggested to prevent corrosion, and hence to improve the long-term performance of ferrocement structures.