INFLUENCE OF BLENDING OF GGBFS ON MECHANICAL PROPERTIES OF CONCRETE
Ground Granulated Blast Furnace Slag (GGBFS) is a by-product of Iron industries and has been used in concrete because of its latent hydraulic property. It also has the advantages over the problems associated with production of the ordinary portland cement (OPC) to our environment. Compared with the normal OPC concrete the GGBFS blended concrete are expected to have enhanced durability that is attributed to improvement in the micro structures, reduction in voids, that make increase in resistance to ingress of aggressive chemicals with moisture or with water. Present study examine weather such attributes could also improve their mechanical properties like compressive, tensile, or bond strength.Cube compressive strength of three mixes are observed upto the age of 180 days, while split and flexural tensile strength are observed only for one mix proportion (medium strength) upto the same age. Bond strength of concrete with different bar diameter is observed for all three mixes at 28 days by pull out test. The parameter varies are percentage of GGBFS blending (0, 10, 30, 40, 50 and 70 percent of total binder), age of concrete (3, 7, 28, 56, 91 and 180 days), diameter of reinforcement (8,10 and 12 mm TMT steel bars) on three concrete with lower, medium and high strength. The OPC is replaced by GGBFS on equal weight basis. All tests are carried out according to the relevant Indian Standards.The results shows that the compressive strength of GGBFS blended concrete are lower than that of OPC concrete at all ages. Cube compressive strength at any age decreased with increase in GGBFS content, which was expected as the content of OPC clinker decreased in total binder content. The rate of reduction in strength with increase in GGBFS content is lesser in concrete mix having lower strength compare to concrete mix having higher strength. This means GGBFS blending is more useful in mixes that having lower binder content or those having lower characteristics strength. Among the various GGBFS content 40 percent blending is found optimum for compressive strength. The compressive strength development in later ages with respect to its 28 day strength is found higher for the GGBFS blended concrete. Strength at 180 day is approximately 117％ of 28 day strength in the case of OPC concrete, while in the case of GGBFS blended concrete this is in the range of 135 to 155％. Strength gain from 28 to180 day is increased with increase in GGBFS content.The split and flexural tensile strength for GGBFS blended concrete is found lower than that of OPC concrete except in some case at 91 and 180 days. The reason of this is the same as for compressive strength. The gain of flexural and split tensile strength after 28 day is found higher in GGBFS blended concrete in comparison to OPC concrete hence it agree with the trends of compressive strength. The optimum GGBFS content form the flexural and split tensile strength point is found between 30 to 40 percent.We compare the flexural and split tensile strength of concrete with the compressive strength at the same age of concrete. For this we taken the expressions given in IS, ACI and in New Zealand standards and calculate the value of constant of expression from experimental results. Average value of these constant for both split and flexural tensile strength is found higher for the GGBFS blended concrete in comparison to OPC concrete, which shows that the tensile strength of GGBFS blended concrete should be higher in comparison to OPC concrete if both have equal compressive strength.Experimental obtained split and flexural tensile strength is found higher than the predicted values from various standards and no relation is hold good at all ages of concrete with same binder content,as value of constant is not equal at all ages of concrete. Hence to get the full advantage of GGBFS blending in structural concrete the blended concrete should be designed for same compressive strength at 28 days.Bond strength of blended concrete is also found lesser in compare to OPC concrete with same reinforcement at 28 days. Bond strength of any concrete with or with out GGBFS get increased with the diameter of reinforcement. Ribs on larger diameter bar are very clearly and sharper in compare to the smaller diameter bar, hence bond due to mechanical bearing of ribs on concrete is proportionally higher. Bond strength of concrete with different GGBFS content also indicates that GGBFS blending is more advantageous in lean concretes having lower strength with lesser binder content and higher water to binder ratio.Increases in the ratio of bond strength to compressive strength are found with GGBFS content in concrete, while the ratios of bond strength to split or flexural strength are nearly same for all concrete These values gives two conclusions that are, the bond strength are directly proportionate to tensile strength of concrete and for same compressive strength the blended concrete developed better bond with reinforcement. This means bond failure is occurred when tensile strength of concrete get exhausted. Higher bond strength of blended concrete is attributed to its higher tensile strength in compare to OPC concrete of same compressive strength. The following conclusions are drawn on the basis of work presented in this paper:·The strength of GGBFS blended concrete at 28 days is lower than that of normal OPC concrete if OPC is replaced by GGBFS on equal weight basis.·The gain in strength from 28 days to 180 days is more in GGBFS blended concrete in compare to normal OPC concrete.·The split and flexural tensile strength of GGBFS blended concrete is higher than that of normal concrete with equal compressive strength. ·The bond strength of concrete is increased with bar diameter.·The bond strength of GGBFS blended concrete is higher than that of normal concrete with equal compressive strength. ·The GGBFS blending is more effective or advantageous with lower strength concrete incompare to with higher strength concrete.·Bond strength of concrete is having more closure relation to its tensile strength rather with compressive strength.
Strength Compressive Tensile Bond Blast furnace slag
Jain, D.K. Prasad, J. Ahuja, A.K.
Department of Civil Engineering, Indian Institute of Technology Roorkee Roorkee, India
国际会议
上海
英文
98-111
2007-05-16（万方平台首次上网日期，不代表论文的发表时间）