High-temperature curing application for concrete comprising fly ash and GGBS M. S. M. Najas, T. Vaseekaran, H. D. Yapa

Fly ash (FA) and ground granulated blast-furnace slag (GGBS) are two promising supplementary cementitious materials (SCMs) that can be used in concrete applications. The early age strength development of such concrete is generally slow; however, the strength reduction can fairly be recovered with high-temperature curing implementation. In this study, the compressive strength behavior of binary and ternary concrete mixes those were subjected to 24 hours 50°C and 70°C curing conditions was explored. Two target compressive strengths levels of 30 MPa and 50 MPa were considered and the SCM blend level was 25 %. The results highlighted that, in terms of early strength achievement, the 50°C curing was favourable for the ordinary Portland cement (OPC) and OPC/GGBS mixes whereas the 70°C curing was attractive in the OPC/FA and in the ternary mixes. For the latter age strength, the high temperature curing detrimentally affected for the OPC and OPC/FA mixes whereas a considerable enhancement was noted for the GGBS blended mixes. The overall effectiveness of the high-temperature curing process was higher in the 30 MPa mixes than in the 50 MPa mixes. Meanwhile, the Arrhenious maturity function based strength predictions were identified to be more accurate than its prediction potential reported for past iso-thermal hightemperature curing applications.

Relationship between flexural and compressive strength of fly ash based geopolymer concrete with ambient curing Bhushan H. Shinde, Bhagyashri S. Nawale, Kshitija Kadam

Fly ash based geopolymer concrete (GPC) requires the temperature curing thus it is limited to precast constructions only. The production of ambient cured fly ash based GPC with treated sea sand will protect the environment from air pollution and depletion of river beds. In this research work, based on the compressive strength, the appropriate percentage of river sand and treated sea sand (i.e. 45 % + 55 %) is evaluated. For gaining the strength of geopolymer concrete in ambient curing (GPCA) as similar to geopolymer concrete with temperature curing (GPCT), ordinary Portland cement (OPC) is added in the dry mix of GPCA and it is found that the 4 % ordinary Portland cement (OPC) is the optimum percentage to obtain the similar strength as geopolymer concrete with temperature curing. In this regards the researchers have investigated the compressive strength, Flexural strength and its power relations. The relations for GPCT, GPCA and conventional concrete (CC) are evaluated by carrying out regression analysis, empirical formula in the form of y = axb and also it compared with the relationship proposed by India, America, Canada, Australia, New Zealand and Europe[6-8] codes of practice for evaluating the flexural tensile strength using compressive strength. It is found that the value of coefficient (a) in empirical equation for GPCT and GPCA are 0.636, 0.574 and the value of power (b) are 0.567, and 0.587 respectively. GPCA and GPCT satisfy the relations proposed by codes of practice of India, America, Canada, Australia, New Zealand and Europe[6-8]. From the overall results it is found that, the fly ash based geopolymer concrete with treated sea sand and 4 % OPC can be best an alternative green concrete to conventional concrete for cast-in-situ construction.

Multi-response optimization of mechanical properties of geopolymer concrete developed using fly ash and Alccofine 1203 Ramya Madhuri B., Srinivasa Rao K.

This paper presents the multi-response optimization of various parameters influencing the mechanical properties of geopolymer concrete. Geopolymer concrete is a sustainable concrete which is prepared by completely replacing ordinary Portland cement (OPC) with fly ash and Alccofine 1203. The main aim of the work is to produce a M30 grade sustainable geoploymer concrete. The binder consists of only fly ash and Alccofine but no OPC, this makes it a sustainable concrete. The number of trials to be conducted are 54 (6 × 3 × 3) as there are six different values for percentage of Alccofine (A), three different values for molarity of NaOH (M) and ratio of Na2SiO3 to NaOH (R) each. But using optimization has reduced the number of trials to 18, nearly 66.67 %, which is remarkable. This saves time, money, resources and man power. And moreover, the percentage error between the predicted values and the experimental results is less than 2 % in majority of the results. The parameters such as proportions of Alccofine and fly ash, molarity of NaOH and the ratio of Na2SiO3 to NaOH are set at their optimum levels to develop a basic M30 grade geopolymer concrete. Initially, the design of experiments (DOEs) is done in Taguchi method using the standard L18 orthogonal array consisting of three factors with different number of levels. After studying the influence of all the variables on individual responses (mechanical properties), the multi-response optimization is performed by using the desirability method, to find out the proportions of all the variables to get the desired responses. The responses considered are compressive strength, split tensile strength, flexural strength, modulus of elasticity (both static and dynamic) and ultrasonic pulse velocity (UPV). The final factors arrived after optimization is 11.6 % of Alccofine in total binder, 12 M NaOH and Na2SiO3 to NaOH ratio of 1.5.

The vitality of temperature control in grout-mix along with control of bleeding Yogita Gaude, K. G. Guptha, T. Mohan

Cementitious grout refers to a predetermined proportion of cement and water used to fill narrow spaces in a variety of construction applications. Long span structures demanding long-term durability throughout their lifespan like pre-stressed bridge sand ducts, the strength, and durability of grout play an important role. Poor quality materials and grouting procedures render voids in the grout systems, eventually leading to premature tendons failure. Therefore, grout must have excellent fresh properties, to maintain the system’s integrity. Bleeding is one such characteristic that should be taken care of at all costs. Grout may be extremely sensitive to temperature changes, particularly when compressive strength is a concern. During temperature changes, casting and pouring concrete necessitate procedures that must be strictly followed and controlled to achieve the desired performance characteristics.

Admixtures including Cebex 100[9], Cebex 200[10], Cebex EN[11] have been introduced in cementitious grouts to improve their fresh state behaviour and studying their behavior towards temperature change to evaluate the strength and durability of grout mix including shrinkage. The study is to assess the efficacy of cementitious grouts for a major river bridge project in Goa, based on their dosage and additives.

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