Experimental Investigation on Fresh and Hardened Properties of High Calcium Flyash Based Geopolymer Concrete

The most important cause of the climate changes in the past few decades are due to the emission of CO2.It may be due to human or natural processes such as disposal of waste material from the thermal power plant, consuming natural resources or production of cement etc. Due to increase in infrastructure created the demand of more construction industries. Increasing importance of environmental protection and energy storage has led to the investigation of alternative binders to replace the cement. Geopolymers are an alternative binder for cement concrete production because of their superior mechanical properties. In the present investigation, for developing the Geopolymer concrete (GPC), high calcium fly ash is used as an alternative binder with Na2SiO3 and NaOH as alkaline liquids. Fresh and hardened properties of GPC are examined by appropriate experiments. Alkaline liquid to High calcium Fly ash ratio (AL: HCF) of 0.45, 0.55,0.6 and 0.65 are used with 8M of NaOH and the developed GPC is kept in ambient curing for 7 days, 28 days, and 56 days. It was observed that with an increase of AL to HCF ratio in the fresh GPC increased the workability of GPC. Increase of AL to HCF ratio in GPC mix increased the compressive strength, tensile strength and flexural strength up to a certain limit.

Experimental study of low carbon emission alternative concrete

Urbanization and mass construction of housing will increase the consumption of cement and available natural resources such as sand and water. The production of cement generated from various industries leads to the emission of carbon dioxide gas in huge quantities into the atmosphere and creates serious problems in handling and disposal. So, the replacement of conventional materials with alternative materials for the preparation of concrete is needed. If the alternative cementitious and industrial waste materials are found suitable in replacing the ingredients of concrete then it can reduce the cost of construction. The present paper represents an experimental study of low carbon emission alternative concrete by replacing conventional concrete materials with alternative materials like geopolymer as binding material, copper and ferrous slag as fine aggregates, steel slag as coarse aggregates, and alkaline solution as an activator. Study made to examine the properties of low carbon emission alternative concrete proposed. The fresh and hardened state characteristics of low carbon emission alternative concrete are evaluated for both oven and ambient curing conditions. It is noticed that the time taken to achieve the strength by oven curing is less than ambient curing but had no major difference in load-carrying capacity and the results obtained are in good concurrence with conventional concrete.

Strength, Fracture and Durability Characteristics of Ambient Cured Alkali—Activated Mortars Incorporating High Calcium Industrial Wastes and Powdered Reagents

Alkali-activated mortars (AAMs) are developed incorporating binary/ternary combinations of industrial wastes comprising of fly ash class C (FA-C), fly ash class F (FA-F) and ground granulated blast furnace slag (GGBFS) with alkaline reagents and silica sand. The use of high calcium precursors, calcium-based powder form reagents, dry mixing method, and ambient curing with performance characterization based on chemical ratios and fracture properties are some novel aspects of the study. The mechanical (dry density, compressive strength, ultrasonic pulse velocity, elastic modulus, fracture/crack tip toughness and fracture energy), durability (shrinkage/expansion and mass change in water and ambient curing conditions, water absorption and freeze-thaw resistance) and microstructural (SEM/EDS and XRD analyses) characteristics of eight AAMs are investigated. The binary (FA-C + GGBFS) mortars obtained higher compressive strengths (between 35 MPa and 42.6 MPa), dry densities (between 2032 kg/m3 and 2088 kg/m3) and ultrasonic pulse velocities (between 3240 m/s and 4049 m/s) than their ternary (FA-C + FA-F + GGBFS) counterparts. The elastic modulus and fracture toughness for mortars incorporating reagent 2 (calcium hydroxide: sodium sulphate = 2.5:1) were up to 1.7 and five times higher than those with reagent 1 (calcium hydroxide: sodium metasilicate = 1:2.5). This can be attributed to the additional formation of C-S-H with C-A-S-H/N-C-A-S-H binding phases in mortars with reagent 2. Ternary mortars exhibited comparatively lower shrinkage/expansion and initial sorptivity indices than their binary counterparts due to the lower geopolymerisation potential of fly ash class F that facilitated the reduction of matrix porosity. All mortar specimens demonstrated 100% or more relative dynamic modulus of elasticity after 60 freeze-thaw cycles, indicating the damage recovery and satisfactory durability due to probable micro-level re-arrangement of the binding phases. This study confirmed the viability of producing cement-free AAMs with satisfactory mechanical and durability characteristics.

Durability Performance On Alkali Activated Metakaolin And Bottom Ash Based Geopolymer Concrete

This paper presents an experimental investigation on the durability properties of metakaolin (MK) and bottom ash (BA) blended geopolymer under different environmental exposure. The blended geopolymer concrete (GPC) was prepared with sodium based alkaline activators under ambient curing temperature. The concentration of sodium hydroxide used was 8M. The ratio of sodium silicate to sodium hydroxide was kept as 2.0. The performance of blended geopolymer concrete was compared with conventional concrete (CC). The test results reveal that blended geopolymer concrete develops a better performance against sulphate and acid resistance. Also, MK- BA GPC shows enhanced performance over the conventional concrete in terms of sorptivity, rapid chloride and water absorption.

Mechanical Properties and Water Stability of High Ductility Magnesium Phosphate Cement-Based Composites (HDMC)

In this study, the compressive test and four-point flexural test were carried out to explore the water stability as well as mechanical properties of high ductility magnesium phosphate cement-based composites (HDMC). The effects of ambient curing age (7 d and 28 d), water immersion age (7 d, 28 d, and 56 d), water/binder ratio (W/B), and magnesium oxide/potassium dihydrogen phosphate ratio (M/P) on the mechanical properties (compressive strength, first-crack strength, ultimate flexural strength, ductility index, and toughness index) and water stability of the HDMC were examined. The results showed that the 28-day ambient curing could lead to higher retention rates of strength, ductility, and toughness than 7-day ambient curing, indicating better water stability; however, it did not result in significant improvement in the mechanical properties of the HDMC. As the water immersion age increased, the mechanical properties of the HDMC with 7-day ambient curing showed an obvious downward trend; the mechanical properties of the HDMC with 28-day ambient curing did not show an obvious decrease and even could be increased in many cases, especially when the water immersion age was 56 days; and the change of water stability was consistent with that of the mechanical properties. If all indexes and their corresponding retention rates were considered comprehensively, the W/B ratio of 0.16 and the M/P ratio of 5 seemed to be the optimum values for the HDMC. The scanning electron microscopy analysis confirmed that the water immersion had a large adverse effect on the HDMC and thus reduced their mechanical properties.

Zero Cement Concrete with Self-Curing Technology: An Overview

Geopolymer concrete is the concept of environmental friendly construction material which helps in reducing the greenhouse gas emission, however it cannot be applied directly on field due to its steam curing process. To overcome this defect various researcher have found self-curing or ambient curing process to achieve same strength as in steam curing process for geopolymer. This paper presents an over review about self-cured or ambient cured geopolymer concrete produced by various methods.

Geopolymer Concrete under Ambient Curing

Geopolymer concrete (GPC) has significant potential as a more sustainable alternative for ordinary Portland cement concrete. GPC had been introduced to reduce carbon footprints and thereby safeguarding environment. This emerging eco friendly construction product finds majority of its application in precast and prefabricated structures due to the special curing conditions required. Sustained research efforts are being taken to make the product suitable for in situ applications. The developed technology will certainly address the issues of huge energy consumption as well reduce water use which is becoming scarce nowadays. Ground Granulated Blast Furnace Slag (GGBS) a by-product of iron industries in combination with fly ash has proved to give enhanced strength, durability as well reduced setting time. This study investigates the effect of GGBS as partial replacement of fly ash in the manufacture of GPC. Cube and cylindrical specimens were cast and subjected to ambient curing as well to alternate wetting-drying cycles. The 28 day compressive strength, split tensile strength, flexural strength and density of GPC specimens were found. The study revealed increase in compressive strength, split tensile strength, density as well flexural strength up to 40 percent replacement of fly ash by GGBS.