Md. Safiuddin

Effects of recycled concrete aggregate on the fresh properties of self-consolidating concrete

Concrete wastes are generally delivered to the landfill sites for disposal. Due to increasing charges of landfill and scarcity of natural coarse aggregate (NCA), recycled concrete aggregate (RCA) derived from concrete wastes is growing interest in construction industry. In the present study, RCA was used as partial and full replacements of NCA to produce self-consolidating concrete (SCC). Different SCC mixes were produced with RCA substituting 0%, 30%, 50%, 70%, and 100% NCA by weight. The water to cement (W/C) ratio and high-range water reducer (HRWR) dosage were kept the same for all concretes. The effects of RCA on the key fresh properties such as filling ability, passing ability, and segregation resistance of SCC were investigated. The test results revealed that the filling ability and passing ability of SCC were improved for 30% and 50% RCA. The SCC mixes with 30% and 50% RCA also possessed adequate segregation resistance. In addition, strong correlations were observed for filling ability, passing ability, and segregation resistance. The overall test results suggest that RCA can be used to produce SCC substituting up to 50% NCA without affecting the key fresh properties of concrete.

State-of-the-art report on use of nano-materials in concrete

Nanotechnology application to concrete presents an innovative approach to improve concrete properties based on the ability to manipulate the cementitious material at an atomic scale. This paper presents a review of the nano-materials that have been used in concrete. The literature survey revealed that four nano-materials are most often used to modify concrete properties; these include nano-silica (nano-SiO2), nano-titanium dioxide (nano-TiO2), carbon nano-tubes (CNTs) and carbon nano-fibres (CNFs). All of these four nano-materials have shown improvement in many concrete properties. Both nano-TiO2 and nano-SiO2 reduce bleeding and segregation, and improve mechanical and transport properties. CNFs and CNTs tend to adversely affect the fresh properties due to agglomerations, which are overcome when a surfactant or ultrasonic mixer is used. However, both CNFs and CNTs significantly improve the mechanical properties of concrete. This paper also discusses how concrete durability is improved when nano-materials are added to concrete. In addition, this paper identifies several research needs based on the gaps in the current state of knowledge on using nano-materials in concrete.

Key Fresh Properties of Self-Consolidating High-Strength POFA Concrete

AbstractSelf-consolidating high-strength concretes, including palm oil fuel ash (POFA), were produced based on the water/binder (W/B) ratios of 0.25–0.40. POFA was used in the concrete mixtures by replacing 0–30% of normal Portland cement by weight. The freshly mixed concrete mixtures were tested to determine the key fresh properties such as filling ability, passing ability, and segregation resistance. Filling ability was measured with respect to slump flow, T50 slump flow time, inverted slump cone flow spread and time, and V-funnel flow time. Passing ability was determined from J-ring flow and L-box flow tests. In addition, sieve and column segregation tests were carried out to quantify segregation resistance. The concrete mixtures were also tested for compressive strength. The experimental results showed that W/B ratio and POFA content had significant effects on the filling ability, passing ability, and segregation resistance of concrete. The filling ability and passing ability of concrete increased wit...

Air Content of Self-consolidating Concrete and its Mortar Phase Including Rice Husk Ash

Abstract This paper presents the air content results of self-consolidating concrete (SCC) and its mortar phase including rice husk ash (RHA) as a supplementary cementing material. Moreover, this paper demonstrates a simple technique to determine the dosage of air-entraining admixture (AEA) required for the target air content in SCC. Different SCC mixtures were designed based on the water/binder (W/B) ratios of 0.30–0.50 and design air content of 4–8%. RHA was incorporated in the concretes substituting 0–30% of cement by weight. The mortars were formulated from the mixture proportions of the corresponding parent concretes and tested to determine the air content at various AEA dosages. The effects of W/B ratio and RHA content on the air content of both mortar and concrete were observed. The effect of mortar volume on the air content of concrete was also noticed. Besides, the AEA dosages required for the target air contents of concrete were estimated based on the equivalent mortar air contents. Later the air...

Air-void Stability in Fresh Self-consolidating Concretes Incorporating Rice Husk Ash

This paper presents the results of experimental study on air-void stability in fresh self-consolidating concretes. Two series of self-consolidating concrete were undertaken for conducting laboratory tests. Each series of concrete included three different fresh mixtures. The air-void stability in fresh concretes was investigated with respect to post-mixing and agitation. The air content of fresh concretes was determined at various test stages and adjusted considering aggregate correction factors. The flowing ability of the fresh concretes was also examined with regard to slump and slump flow. The entire testing period involved four stages extended to 60 and 90 minutes for series 1 and 2, respectively. Test results reveal that the slump and slump flow of the concrete mixtures were consistent in all test stages, and the loss of air content was minimal. The maximum loss of air content over the period of 60 and 90 minutes was less than 1.0%. Rice husk ash did not affect the air-void stability in fresh concretes. However, it increased the demand for high-range water reducer and air-entraining admixture. The overall test results indicate that the air-void stability in all fresh self-consolidating concretes was satisfactory.

Effects of Medium Temperature and Industrial By-Products on the Key Hardened Properties of High Performance Concrete

The aim of the work reported in this article was to investigate the effects of medium temperature and industrial by-products on the key hardened properties of high performance concrete. Four concrete mixes were prepared based on a water-to-binder ratio of 0.35. Two industrial by-products, silica fume and Class F fly ash, were used separately and together with normal portland cement to produce three concrete mixes in addition to the control mix. The properties of both fresh and hardened concretes were examined in the laboratory. The freshly mixed concrete mixes were tested for slump, slump flow, and V-funnel flow. The hardened concretes were tested for compressive strength and dynamic modulus of elasticity after exposing to 20, 35 and 50 °C. In addition, the initial surface absorption and the rate of moisture movement into the concretes were determined at 20 °C. The performance of the concretes in the fresh state was excellent due to their superior deformability and good segregation resistance. In their hardened state, the highest levels of compressive strength and dynamic modulus of elasticity were produced by silica fume concrete. In addition, silica fume concrete showed the lowest level of initial surface absorption and the lowest rate of moisture movement into the interior of concrete. In comparison, the compressive strength, dynamic modulus of elasticity, initial surface absorption, and moisture movement rate of silica fume-fly ash concrete were close to those of silica fume concrete. Moreover, all concretes provided relatively low compressive strength and dynamic modulus of elasticity when they were exposed to 50 °C. However, the effect of increased temperature was less detrimental for silica fume and silica fume-fly ash concretes in comparison with the control concrete.

Sound Absorption and Friction Responses of Nanoconcrete for Rigid Pavements

This paper reports the influence of nanosilica on friction and sound absorption responses of concrete for application in rigid pavements. The paper also discusses the feasibility of applying nano-lotus leaf as a coating for concrete material. Previous research on friction and sound absorption characteristics of concrete pavement primarily emphasized creating different surface textures through macrotexture modifications. The microstructure can also have a significant effect on surface texture, friction, and sound absorption characteristics of concrete. This research studied the friction and sound absorption properties of concrete on the basis of microtexture modification that used nanomaterials such as nano-silica and nano-lotus leaf. Several laboratory concretes were produced by using different proportions of nanosilica, which partially replaced cement by weight. The fresh concretes were tested for workability, wet density, and air content. The hardened concretes were tested for compressive strength, friction, and sound absorption. The British pendulum test was used to determine the friction number. An impedance tube was used to determine the sound absorption coefficient. Preliminary results indicate that nanosilica can increase friction and sound absorption of concrete pavements. In addition, the results show that nano-lotus leaf can be applied as a coating on concrete material for rigid pavements to improve retention of their friction properties during the wet season.

Chloride penetration resistance of concrete sealer and coating systems

AbstractThis study investigated the chloride penetration resistance of a silane-based sealer (SS1), an acrylic-based coating (AC1), and two cementitious coatings (CC1 and CC2) when applied on concrete surface. Concrete powder samples were collected from 15, 30 and 45 mm depths of sealer and coating treated concrete prism specimens, which were exposed to H2O and de-icing solutions of NaCl, Geomelt S30, MgCl2 and CaCl2 for 100 freeze-thaw cycles followed by 25 wet-dry cycles. Chloride analysis was carried out to determine the total water-soluble chlorides of concrete. Test results revealed that the chloride penetration for exposure to the de-icing chemicals occurred at a depth of 15 mm from the concrete surface. The highest chloride penetration occurred for the non-treated concrete. The sealer ‘SS1’ exhibited good performance except with exposure to NaCl solution. Among the three different coating products, the acrylic-based coating ‘AC1’ was the best-performing coating, whereas the cementitious coating ‘CC...

Water vapor transmission and waterproofing performance of concrete sealer and coating systems

AbstractThis paper reports the water vapor transmission and waterproofing performance of a silane-based penetrating sealer (PS), two cementitious coatings (CC1 and CC2), and a polymeric coating (PC). The sealer and coating products were applied on 100-mm concrete cubes. In total, fifteen concrete cubes including the control specimens were prepared. The treated concrete cubes were tested to determine the ability of the selected products to improve waterproofing and to transmit water vapor. The correlation between water vapor transmission and waterproofing performance was also examined. Experimental results revealed that the cementitious coating CC2 had the lowest degree of water vapor transmission but the highest degree of waterproofing performance. In contrast, the highest degree of water vapor transmission but the lowest degree of waterproofing performance were observed for the cementitious coating CC1. The penetrating sealer PS provided greater water vapor transmission but lower waterproofing ability th...