With an increased usage of high strength concrete (HSC) in general structural construction and its application in power, nuclear and oil industries where structures are subjected to elevated temperatures and in the event of accidental fires, it is essential to investigate its behaviour. There is a serious lack of fire test data for HSC subjected to thermal cycles and hence it is important to study the mechanical properties of HSC compared to normal strength concrete.
This paper presents the study of residual compressive strength and weight loss of high strength concrete compared to normal strength concrete of age 28 days subjected to thermal cycles namely 1, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 apart from control concrete. Specimens were exposed to temperatures from 100 to 400°C for 8 hours exposure duration and subsequent air cooling for the remaining period of day. Therefore, one thermal cycle consists of 8 hours heating and 16 hours cooling. The results obtained can be useful as guidelines for fire resistant design of the structures subjected to heating and cooling cycles at elevated temperatures.
Industrial wastes material such as GGBFS may be used to exchange partially cement amount in concrete. This research paper investigates the probability of replacing high volume of GGBFS as a cement substitute in concrete. In this present investigation, cement was replaced by GGBFS in 50% and 60% and concrete mix proportions was obtained for M30 grade concrete according to IS 10262: 2009 guidelines. The compressive strength, split tensile strength, flexural strength, shear strength and impact strength test were done for the concrete cured with different curing techniques.
Concrete is the most common durable material used in construction industry. Durability is an important parameter when structural reinforced concrete is used in harsh environments. The environmental factors such as weathering action, chemical attack, abrasion and other deterioration process may change the properties of reinforced concrete with time. The degrees of deterioration occurs is mainly due to the presence of pore size in the concrete. Concrete with Supplementary Cementitious Material (SCM) like Metakaolin (MK) and Nano Silica (NS) will help in producing the concrete with a dense microstructure, which will decrease the voids in concrete. Experimental study was carried to study the effect of Metakaolin in M25 and M50 grade concretes by replacement of cement by weight at different proportions like 0%, 5%, 10%, 15%, 20%. Further, the influence of Nano Silica was studied in these concretes by adding 0.5%, 1%, 1.5% and 2% by weight of cementitious materials. Increase in compressive strength of 44.4% and 26 % for the corresponding control concrete of M25 and M50 grades respectively was observed maximum with 10 % replacement level of Metakaolin by weight of cement. Addition of 1.5% Nano Silica in M25 grade concrete showed higher strength which is 74% higher than the control concrete. In M50 grade concrete the maximum strength was observed with the addition of 2.0 % of Nano Silica which showed 48 % higher than the control concrete. Combination of the optimum percentage of MK and NS addition show good enhancement in the mechanical properties when compared to control and MK based concrete but slight marginal decrease when compared to NS based concrete for both the grades.
The presence of high workability, durability and strength, are what qualifies concrete to be termed as high performance concrete. The rising need for high performance concrete in the construction industry, globally, has necessitated the exploration of different means to enhance concrete to this level of optimum performance. Durability can be improved through the use of supplementary cementitious materials. High volume fly ash (HVFA) is known to improve the durability of high strength concrete and Nanosilica (NS) efficiently improves the strength. This paper studies the efficiency of HVFA and NS in reducing the voids in concrete and this is ascertained through the means of a wet packing density test. The two part test involved determining the optimum packing density (PD) of concrete containing cement content from 13% to 21% at 2% intervals along with varying w/c ratios, in the first part. The second part involved replacing the cement content for a particular w/c ratio which produced maximum reduction in void ratio with 50% fly ash by weight. The HVFA concrete was also introduced with NS in varying percentages from 1% to 4% at an interval of 1% by weight of cementitious material. The test indicates a positive outcome in terms of reduction in voids by high volume fly ash and NS to a large extent.
Concrete is mostly widely used construction material today. Other than its hardened properties, its behavior in green state affects the constructability and economics to a great extent. Modern concrete uses various supplementary cementitious materials, either as replacement of cement or as additive to enhance behaviour of concrete, both in hardened state and in green state, to improve its structural behaviour along with its economics and sustainability in green state, concrete needs enough consistency to be transported, placed, consolidated and finished in structural forms. The property of concrete in green state which controls its ease in transportation, placement, consolidation and finishing depends on rheology of material. The rheology of concrete, not only affect the cost, but also affects structural and durability behavior of resulting structure in the longer run. Other than aggregate mass, paste rheology principally affects the rheology of concrete. The paper investigates the effect of fly ash, most commonly used supplementary cementious material, as cement replacement on blended paste rheology. It examines the influence of three variables of fly ash, fineness, replacement levels, and waterbinder ratio on the yield stress and viscosity of blended pastes.
Some special concretes need the ability to flow, pass through small spaces and at the same time should be able to detour through the congested spaces in the structural elements. Research and Development of new/special concretes which can overcome such problems and provide good serviceability and durability is one of the major thrusts on the construction engineers and industry today. Self Compacted Concrete is one such special concrete which can answer such problems. Originally developed in Japan, this concrete can tackle the workability and durability issues without sacrificing the strength. One of the major challenges the concrete industry is facing today is sustainability. Use of Quartz powder in SCC is one such mineral which can contribute to sustainable construction. The workability of Self Compacted Concrete is too sensitive to solid formation change and fiber addition in Self Compacting Concrete will decline the fresh properties of concrete. Mineral admixtures like micro silica and quartz powder and chemical admixtures like super-plasticizers can enhance the workability of fibrous SCC. A detailed experimental investigation is carried out to develop High Strength Hybrid Fibre Reinforced Self Compacting Concrete (HSHFSCC) with the optimum fibrous powder content is obtained by working on various dosages of steel and glass fibres. A dosage of 1.5 % (0.75 % steel + 0.75% glass fibres by weight) is arrived satisfying the fresh and hardened properties.
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