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This paper presents the surface water absorption of self-compacting concrete (SCC) containing fly ash and silica fume using sorptivity test. Ordinary Portland cement was partially replaced by various combinations of fly ash and silica fume. Test results show that the presence of fly ash and silica fume significantly reduce the surface water absorption of self-compacting concrete at a water-binder ratio of 0.38. When only fly ash is used to partially replace Ordinary Portland cement, a more noticeable reduction in sorptivity is found when the fly ash content is greater than 20%. The effect of combined use of fly ash and silica fume on reducing the water absorption and sorptivity is much more significant than using fly ash only. Moreover, it is noted that increasing the proportion of fly ash and silica fume leads to an enhanced reduction in water absorption. The addition of fly ash and silica fume, in general, increases the 28-day cube strength. However, there is no correlation between the compressive strength and the sorptivity in SCC achieved.

Ordinary concrete is generally considered to have satisfactory fire resistance but when it comes to high strength concrete it shows extensive damage or even catastrophic failure at elevated temperatures. This research work was carried out to evaluate the performance of High Performance Concrete (HPC) made with Fly ash (FA) and Metakaolin (MK) at elevated temperatures. Variables of the test program include partial replacement of cement with MK from 5% to 20%, FA from 20% to 60%, temperatures from 27 °C to 800 °C and two types of cooling methods (in air and water). The mechanical performance was assessed from compressive strength while the durability was assessed from chloride permeability and water sorptivity tests. Mass loss at elevated temperatures was also determined. Moreover, quantitative analysis of the SEM images on selected concrete specimens was performed using Image Pro-plus software. Test results showed degradation in the mechanical and durability properties of HPC at elevated temperatures. Quick cooling produced greater loss in compressive strength than slow cooling. This is because of the effect of thermal shock which was more pronounced at 400 °C. From the standpoint of durability, all mixes showed major increase in charge pass and sorptivity values in between 400 °C and 600 °C. Therefore, 400 °C could be regarded as the critical temperature for change in the properties of HPC. Quantitative analysis of the SEM images of Interfacial Transition Zone (ITZ) indicated that pore area fraction increased with the increase in temperature. This resulted in the degradation of microstructure and affected the strength and durability of concrete. In general, at temperatures (400 °C and above) FA20 showed better performance while MK mixes (MK10 and MK20) showed higher degradation in terms of durability. This gives an indication that MK mixes should be used with care especially in structures which may be subjected to temperature of 400 °C and above.

The extensive use of eco-friendly materials in concrete has led to the demand to fully understand the effect of fire on concrete. This research was carried out to evaluate high performance concrete (HPC) made with fly ash and metakaolin with replacement level of 20 percent by weight of cement after elevated temperatures exposure (200 °C, 400 °C, 600 °C and 800 °C). The mechanical performance was assessed from compressive strength while the durability was assessed from chloride permeability and water sorptivity test. Qualitative analysis of the microstructure of heated and unheated concrete was performed by SEM while quantitative analysis was performed on SEM images using Image Pro-plus software. Based on the qualitative and quantitative analysis of SEM images, the distribution of the number, type and surface area fraction of flaws were identified and changes in the structure of Interfacial Transition Zone (ITZ) were classified into different temperature ranges. Test results show that for all mixes post-elevated temperature compressive strength decreased while charge passed and sorptivity values increased with the increase in temperature from 27 °C to 800 °C. For all mixes, major strength and durability loss occurred after 400 °C. Therefore, 400 °C can be considered as critical temperature from the standpoint of strength and durability loss. From the qualitative and quantitative analysis, different types of flaws were identified. These were texture flaws (T), orientation flaws (O) collectively called as textured and orientation flaws (TO) and local flaws (L). The post-elevated temperature surface area fraction of TO and local flaws in the ITZ of each concrete mix continuously increased with the increase of elevated temperature. The increase in surface area fraction of flaws resulted in gradual loss in the mechanical and durability properties of concrete. Major increase in surface area fraction occurred in between 400 and 600 °C, resulting in major strength loss and sharp increase in charged passed and sorptivity values through concrete specimens. Therefore, 400 °C can be regarded as critical for change in the properties of concrete. No specific relationship between the number of TO flaws and the type of binding material in concrete and the temperature was found. However for local flaws, in general, the number increased with the increase of temperature. Also, the changes in the structure of ITZ were classified into three temperature ranges namely; the low range temperatures (27–200 °C), the medium range temperatures (200–400 °C) and the high range temperatures (400–800 °C). The physical character of ITZ in HPC changes gradually from a discrete or discontinuous flaw zone at normal or mildly elevated temperature to a continuous and highly porous flaw zone at elevated temperatures. Thus, the classification signifies the effect of the texture of coarse aggregate and the orientation of fine aggregate in concrete matrix coupled with the effect of elevated temperatures on ITZ of HPC.

An experimental investigation was carried out to evaluate the performance of Fly Ash (FA) and Metakaolin (MK) mortar at elevated temperatures. Variables of the test program include partial replacement of cement with MK from 5% to 20%, FA from 20% to 60% and temperatures from 27 °C to 800 °C. The mechanical performance was assessed from compressive strength while the durability was assessed from chloride permeability test. Qualitative analysis of the microstructure of heated and unheated mortar was performed by Scanning Electron Microscope (SEM) while quantitative analysis was performed on SEM images using Image Pro-plus software. Test results show that for all mixes compressive strength decreased while charge passed increased with the increase in temperature from 27 °C to 800 °C. For all mixes, major strength and durability loss occurred after 400 °C. Therefore, 400 °C can be considered as critical temperature from the standpoint of strength and durability loss. Qualitative and quantitative analysis of SEM were found to be consistent with the results of strength and durability loss. The observation of SEM images and image analysis of area fractions of hardened cement paste (hcp) of different mortar mixes indicated that with the increase in temperature the pore area fraction increased while hydrated paste area fraction decreased. These factors resulted in the degradation of microstructure and affected the strength and durability of mortar. Major drop in hydrated paste area and rise in pore area fraction occurred at 400 °C. Therefore, 400 °C could be regarded as the critical temperature for change in the properties of mortar. In general, fly ash mix (FA20) showed better performance in all aspects.

This research work was carried out to evaluate the performance of High Performance Concrete (HPC) made with Fly Ash (FA) and Metakaolin (MK) at elevated temperature through Stiffness Damage Test (SDT). Variables of the test program include partial replacement of cement with MK (10% and 20%) and FA (20% and 40%) and temperature from 27 to 400 °C. To quantify the damage, chord loading modulus, unloading stiffness, plastic strain, damage index and non-linearity index were evaluated from SDT. Correlation among SDT parameters and in between SDT parameters and elevated temperature were also studied. According to the test results, the SDT parameters showed that the stiffness and elasticity decreased and damage increased with the increase in temperature. The stiffness changes were evident from chord modulus and unloading stiffness, elasticity changes from plastic strain and damage to concrete from damage index. For all mixes, significant change in the SDT parameters occurred at 300 °C. Therefore, 300 °C can be considered as critical temperature. At elevated temperatures (300 °C and 400 °C), FA mixes showed lower values of plastic strain and damage index than MK mixes. Thus, it may feasible to increase the allowable working temperature for FA mixes. The SDT parameters were found to be sensitive to elevated temperatures caused by changes in the microstructure of concrete. Test results also revealed that plastic strain and damage index correlate well with loading elastic modulus with values of coefficient of correlation equal to 0.9657 and 0.9835 respectively. Therefore, plastic strain and damage index measured from SDT can be used to estimate the percentage residual chord loading modulus of concrete affected by fire. Strong correlation also exists between PS and DI with coefficient of correlation equal to 0.985.

This paper examines the water permeability and chloride penetrability of self-compacting concrete with fly ash and silica fume as admixtures. The influence of 28-day concrete strength on concrete permeability is also investigated. It was found that addition of fly ash and silica fume was effective in reducing the concrete permeability. Most self-compacting concrete specimens showed low to very low water permeability and chloride penetrability. Test results also indicated that the 28-day concrete strength should not be used as an indicator for concrete permeability.

An experimental study on the compressive strength and carbonation depth of lightweight concrete mixes that contain pulverized fuel ash (PFA) and silica fume (SF) as cement replacements is presented in this paper. Mixes that had a relatively high replacement level of PFA at 25, 40, and 55% and of SF at 5, 10, and 15% by weight were compared. The results indicated that accelerated curing at 60 °C for 3 days improved the 28-day compressive strength of the PFA- and SF-incorporated mixes but resulted in higher carbonation of the mixes compared with that under normal temperature curing. Mixes that had 25% PFA or 5–10% SF as partial cement replacements had slightly higher strength under accelerated curing and slightly lower strength under normal curing than the control mix. At higher replacement levels of PFA and SF, further lower strength and higher carbonation was observed.

This paper presents a study on accelerated carbonation testing of normal weight concrete (NWC) and lightweight concrete (LWC) mixes proportioned for three levels of strength grades. Two types of curing regimes were applied; (1) hot curing in water at 60 C for 3 days and (2) normal curing in water at 27 C for 28 days. Pulverized fuel ash (PFA) at 25% and silica fume (SF) at 5% and 10% replacement of ordinary Portland cement (OPC) in concrete were utilized to blend binary and ternary mixes in addition to OPC mixes. The results indicated that the effect of hot water curing on compressive strength development was more prominent in PFA/SF incorporated mixes than OPC mixes. The carbonation of LWC mixes was lower than NWC mixes at similar strength levels. The mixes with 25% PFA had marginally higher carbonation than OPC mixes under both hot and normal curing. The incorporation of SF in concrete mixes also increased the carbonation. Mixes under hot water curing had higher carbonation than mixes under normal curing. 2007 Elsevier Ltd. All rights reserved.

Polystyrene aggregate concrete (PAC) is a lightweight concrete with good deformation capacity, but its application is usually limited to non-structural use because of its apparent low strength properties. The present study is an effort to develop a class of structural grade PAC with a wide range of concrete densities between 1400 and 2100 kg/m 3 through partial replacement of coarse aggregate with polystyrene aggregate (PA) in control concrete. Extensive laboratory tests have been carried out and the focus of this paper is to characterize the strength and long-term drying shrinkage properties of PAC. The parameters studied include PA content and curing conditions. The results show that the concrete density, concrete strength and elastic modulus of PAC decrease with increase of PA content in the mix. From the calorimetric test results, the increase in strength acceleration of PAC at early ages is due to the low specific thermal capacity of polystyrene aggregate. Besides, the long-term shrinkage and swelling of PAC are highly dependent on the PA content and the duration of water curing. Owing to the non-absorbent property of polystyrene aggregate, the ratio of reversible shrinkage to drying shrinkage observed for PAC was lower compared to the control concrete.

The workability and mechanical properties of self-compacting lightweight concrete and normal self-compacting concrete have been studied. Self-compacting lightweight concrete with a binder content of 500–650 kg m−3 and a density of 1650 kg m−3 was made using less superplasticizer and viscosity modifying agent and a lower water/binder ratio than normal self-compacting concrete. The bulk density was only 75% of normal self-compacting concrete but with a similar compressive strength. The elastic modulus was about 80% of that of normal self-compacting concrete. These results indicate that self-compacting lightweight concrete is excellent in workability and has a lower density, a higher compressive strength and a relatively high elastic modulus than normal self-compacting concrete using the same design principles.

Air entraining agent is used to control the floatation of lightweight aggregate (LWA) in lightweight aggregate concrete (LWAC), therefore reducing the segregation of LWAC. At the same time, using an air entraining agent will affect the water sorption of the concrete. In this paper, two lightweight concrete mixes of density 1000 kg/m 3 and air content of 13.5% and 31.9% were compared and the effects of entrained air on the strength, surface sorptivity, and chloride permeability of LWAC are presented. Results show that the use of porous LWA would not lower the permeability resistance of concrete. Entrained air had little effect on sorptivity but a major effect on chloride permeability. The weaker pores' network in the cement paste is the basic cause for the high chloride permeability of concrete than the use of porous LWA. Although chloride permeability of low density LWAC concrete decreased with age of concrete, it was found that the concrete was not dense enough to stop the chloride ion to penetrate through the concrete before the concrete mature at 90 days.

This paper investigates the effect of elevated temperature on the flexural strength (FS) and split cylinder strength (SCS) of high strength concrete (HSC). Four concrete mixes of 50, 90, 110, and 130 MPa grade were prepared and subjected to elevated temperature exposure of 200°C and 400°C, and cooled under slow and quick cooling conditions. In addition, 130 MPa grade concrete specimens were also subjected to 100°C and 600°C exposure temperatures to compare FS and SCS under elevated temperatures. It was observed that with the increase in the elevated temperature, the FS and SCS experienced significant losses. The loss was found to be higher for richer concretes. FS was observed to experience a sharp loss at low temperatures that became gradual later at high temperatures. SCS, however, experienced a gradual loss, though sharper than FS, with the increase in temperature. The results indicated that cooling had a significant effect on the residual values and quick cooling caused greater loss in FS and SCS, than slow cooling at elevated temperatures. The quick cooling was noted to produce maximum loss over slow cooling at temperatures around 400°C.