Cold-bonded Fly Ash Aggregate Research Articles

Effect of Nanosilica on the Strength and Durability of Cold-Bonded Fly Ash Aggregate Concrete

Cold-bonded Fly Ash Aggregate (CFAA), as an alternative to natural coarse aggregates, can prepare more lightweight, economical, and sustainable concrete. However, CFAA concrete has insufficient durability, which hinders its application in a salt-corrosion environment. Nanosilica (NS) has an advantage of high activity and is generally used as an efficient mineral admixture in engineering. This study aims to improve the strength and durability of CFAA concrete by incorporating NS. To this end, compression tests, splitting tensile tests, and microscopic analyses were performed to investigate the mechanical properties of the concrete containing different NS dosages. Subsequently, the dry–wet and freeze–thaw durability tests were conducted to evaluate the salt-corrosion resistance and the frost resistance in the water, Na2SO4 solution, and Na2CO3 solution. The results show the compressive and splitting tensile strength peak at 2 wt% NS dosage. In this instance, the concrete has an optimum microstructure and exhibits desirable salt-corrosion resistance in the late stage of dry–wet cycles. During freeze–thaw cycles, NS could improve the frost resistance of the concrete but scarcely diminished internal damage under sulfate attack. The study explores the long-term performance of NS-modified CFAA concrete, providing a simple and effective method to mitigate the concrete deterioration in a harsh environment.

Properties of concrete containing high-calcium fly ash artificial aggregate

The work aims to develop a concrete mixture with cold-bonded fly ash aggregate based on high-calcium fly ash and experimentally study its physical and mechanical properties. The results of experimental studies of concrete with artificial coarse aggregate based on fly ash from Berezovskaya Thermal Power Plant showed compressive strength of 28.92 MPa, flexural strength of 4 MPa, coefficient of linear thermal expansion of 14.5 * 10−6 K−1, modulus of elasticity of 16 *109 Pa, heat of hydration on the 10th day - 340 kJ/kg, shrinkage deformation of −1.8 mm/m. It has been established that heat treatment of fly ash aggregate for 8 hours at a temperature of 80 °C after 7 days of air storage did not positively affect the physical and mechanical properties of concrete. The compressive strength at the age of 28 days and the modulus of elasticity of the specimens with coarse aggregate after heat treatment were lower by 41% than that of the control mixture.

Influence of design parameters on engineering properties of angular shaped fly ash aggregates

Fly ash of thermal power plants substitute’s construction materials and can help to preserve non-renewable resources. In the construction industry, more particularly in concrete and road construction, a huge quantity of aggregate is being used. Fly ash aggregate is a unique alternative for the construction industry at present. However, the properties of fly ash aggregate are mostly controlled by the type and dosage of additive used besides the characteristics of ash and curing method adopted. In the present study, specimens from various combinations of fly ash with hydrated lime, ground granulated blast furnace slag, and cement were prepared at maximum dry unit weight with optimum moisture content and cured by hot water curing method. The cured specimens were crushed to prepared angular shaped fly ash aggregates. The influence of the binding additives on the unconfined compressive strength of mixes and aggregate impact value was studied. Measured engineering properties were also analyzed through a micro-level study. The addition of lime enhanced the unconfined compressive strength of mixes and impact value of aggregates, whereas, replacement of lime with the ground granulated blast furnace slag and cement reduced the strength of the mixes. Unconfined compressive strength value of mixes shows the inverse relationship with impact value of aggregate prepared from that mixes and a correlation between unconfined compressive strength and aggregate impact value has been proposed. Moreover, the effect of moisture content and pressing force on compressive strength and aggregate impact value was also investigated on optimum mixes. From these experimentations, the optimum combinations of fly ash-additive mixes, the optimum value for moisture content, and pressing force were chosen; and angular shaped fly ash aggregates were produced by hot water curing method. Furthermore, the various physical properties, mechanical properties and durability index of these fly ash aggregates are discussed and compared with the Indian standard specifications. The leaching behavior of these aggregates was also examined in this study. The addition of lime gives better results compared to cement and ground granulated blast furnace slag and use of lime seems to be more cost-effective. Thus, these cold bonded fly ash aggregates with significant strength may find prospective use in civil engineering construction sector.

Impact resistance of concrete produced with plain and reinforced cold-bonded fly ash aggregates

In this paper, the impact resistance of concrete produced with cold-bonded fly ash aggregates (FAAs) in partial or full replacement, by volume, of crushed limestone coarse aggregates was investigated. Fly ash aggregates were produced as plain (PFAA), with 0.1% crumb rubber (CRRFAA) and with 0.1% polypropylene fibers (PPFRFAA), by weight, as reinforcement. Nine concretes are produced at w/c of 0.40 by replacing crushed stone coarse aggregate at 4–8 mm, 8–16 mm and 4–16 mm size fractions with fly ash aggregate together with the control concrete having a target compressive strength of 50 MPa. While use of different types of FAAs resulted in slight to substantial decrease of compressive and splitting tensile strengths and impact resistance of concretes, higher values are obtained in concretes with FAAs replacing 8–16 mm size group of crushed stone coarse aggregate. Polypropylene fiber and crumb rubber addition into the fly ash pellets increased the ability of the aggregates to absorb energy and thus the impact resistance of concrete. The polypropylene fibers protruding from the surface of FAAs might have caused better adherence of the FAAs to the cement paste to result in higher impact resistance.

Cold-bonded fly ash aggregate concrete

Cold-bonded fly ash aggregate concrete

Influence of curing method on characteristics of environment-friendly angular shaped cold bonded fly ash aggregates

A large quantity of natural aggregate is being used for the construction of roads, buildings, and mega-structures that affect the environment. It is also noticed that the scarcity of good quality aggregate in some regions of the country leads to an increase in the cost of aggregates. Some efforts have been made to find out a substitute for natural coarse aggregates. Several processes for the production of fly ash aggregates have been developed in the past and some of these were commercialized. These processes are very costly and time-consuming resulting in the non-use of these aggregates on a large scale in civil engineering applications. It is also found that the pelletization process manufactures round-shaped aggregates that have negligible interlocking properties leading to lower load-bearing capacity. In this study, the effect of various curing methods on the strength of fly ash-lime mixes are investigated through the unconfined compressive strength, aggregate impact value, X-ray Diffraction pattern, and scanning electron microscope images. From this study, the hot water curing method has been found as more effective for the hardening of the fly ash aggregates and suggested for further study. Secondly, the rapid and economical four-step process for the production of angular shaped high strength fly ash aggregate has been proposed in the paper. This method for producing fly ash aggregate comprises simple four steps of mixing, compaction, curing, and crushing. The aggregates made with the said process have dense structure, angular in shape for better interlocking, excellent mechanical properties such as toughness and hardness, and high durability. These aggregates also fulfill the Indian specifications for road aggregate and the requirement of structural concrete aggregates. The bulk utilization of this fly ash aggregates in the civil infrastructures can solve two problems with one effort: (a) Fly ash disposal problem and (b) Provision of needed construction aggregates, thus protecting natural diminishing resources of aggregates.

Sustainability evaluation of cold-bonded aggregates made from waste materials

Cold-bonded aggregates are technically feasible alternatives to conventional crushed stone aggregates (CSA) in concrete production, but the sustainability of cold-bonded aggregates has not yet been studied. Therefore, this paper suggests a framework for evaluating the sustainability of cold-bonded aggregates. The three pillars of sustainability, namely, social, environmental and economic factors, were used as the main criteria in the evaluation process. Cold-bonded aggregates made from waste materials such as fly ash and quarry dust were used in this study. The sustainability indices of cold-bonded fly ash aggregate (CBFAA) and cold-bonded quarry dust aggregates (CBQDA) were determined and compared with that of CSA. Fourteen sub-criteria were identified for this study. Out of the 14 sub-criteria, six sub-criteria were identified as social factors, another six were identified as environmental factors and two were identified as economic aspect factors. OF the 14 sub-criteria, eleven sub-criteria were qualitative in nature and three were quantitative. A qualitative assessment was conducted via a questionnaire survey of 254 registered practicing engineers. A quantitative evaluation of the embodied energy, lifecycle cost (LCC) and capital cost was performed in this study. The multi-index comprehensive analysis model was used to compute the sustainability indices of different types of coarse aggregates. The sustainable indices of CSA, CBFAA and CBQDA were found to be 0.610, 0.737 and 0.789, respectively. This result indicates that cold-bonded aggregates are sustainable and can be considered for used concrete production. The sensitivity analysis results indicated that the amount of binder and distance to the source of raw materials are important aspects. The framework developed in this study can be used to evaluate other building materials that are relatively new in origin.

Developing geopolymer concrete by using cold-bonded fly ash aggregate, nano-silica, and steel fiber

This experimental study presents the effect of nano-silica and steel fiber on the transport properties and compressive strength of alkali-activated slag/fly ash concrete incorporated cold-bonded fly ash aggregate. In order to reduce energy consumption and provide environmental impact, the cold-bonded process was used to manufacture cold-bonded fly ash aggregate. Twenty four geopolymer concrete mixtures incorporated cold-bonded fly ash aggregate, nano-silica, and steel fiber were produced with sodium hydroxide concentration of 12 M and cured at ambient temperature. Transport properties of geopolymers were examined through water penetration, water sorptivity, and gas permeability at 28 and 90 days. Results indicate that geopolymer concrete incorporated cold-bonded fly ash aggregate can be produced with compressive strength as high as 28.23 and 36.62 at 28 and 90 days, respectively. However, 2% nano-silica and 1% steel fiber volume fraction were the most significant parameters that caused remarkable improvement of investigated properties. Moreover, the incorporation of waste materials in aggregate and geopolymer concrete production can alleviate environmental problems.

Effect of silica fume and steel fiber on the mechanical properties of the concretes produced with cold bonded fly ash aggregates

This paper reports an experimental study on the mechanical properties of steel fiber incorporated plain and silica fume (SF) concretes produced with cold bonded artificial fly ash aggregates (AFAs). Two concrete series with water-to-binder (w/b) ratios of 0.35 and 0.55 were designed. SF incorporation was achieved by 10% replacement of the weight of cement by silica fume. Two types of hooked-end steel fibers with length/aspect ratios of 60/80 and 30/40 were utilized. AFA, produced from cold bonding pelletization of 90% class F fly ash and 10% Portland cement, was used as coarse aggregate in all of the concrete mixtures. The mechanical properties investigated were compressive strength, modulus of rupture, and bonding strength between rebar and concrete. The tests were carried out at the end of 28day water curing. Analyses of variance of the experimental results were performed and the contributions of the significant factors on the mechanical characteristics of the concretes were determined for statistical evaluations. Moreover, correlation of the experimental data was carried out to monitor the interaction between mechanical properties and bonding strength of the concretes. The results demonstrated that incorporation of SF and utilization of different types of steel fiber reinforcements significantly affected the mechanical properties of the concretes regardless the w/b ratio.

Strength and elastic properties of structural lightweight concretes

The study presents the influence of characteristics of four aggregate types (two sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight crushed limestone aggregate) on the strength and elastic properties of concrete mixtures. Different models were also used in order to predict the strength and modulus of elasticity values of concretes. The results of this study revealed the achievement of manufacturing high-strength air-entrained lightweight aggregate concretes using sintered and cold-bonded fly ash aggregates. In order to reach target slump and air content, less amount of chemical admixtures was used in lightweight concretes than in normal-weight concrete, leading to reduction in production cost. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production slightly decreased the strength. The models given by codes, standards and software and equation derived in this study gave close estimated values to the experimental results.

Influence of fly ash on strength and sorption characteristics of cold-bonded fly ash aggregate concrete

Cold-bonded fly ash aggregate concrete with fly ash as part of binder or fine aggregate facilitates high volume utilization of fly ash in concrete with minimum energy consumption. This paper investigates the influence of fly ash on strength and sorption behaviour of cold-bonded fly ash aggregate concrete due to partial replacement of cement and also as replacement material for sand. While cement replacement must be restricted based on the compressive strength requirement at desired age, replacement of sand with fly ash appears to be advantageous from early days onwards with higher enhancement in strength and higher utilization of fly ash in mixes of lower cement content. Microstructure of concrete was examined under BSEI mode. Replacement of sand with fly ash is effective in reducing water absorption and sorptivity attributable to the densification of both matrix and matrix–aggregate interfacial bond. Cold-bonded fly ash aggregate concrete with a cement content of 250 kg/m 3, results in compressive strength of about 45 MPa, with a total inclusion of around 0.6 m 3 of fly ash in unit volume of concrete.

Effect of curing method on characteristics of cold bonded fly ash aggregates

This paper discusses the influence of normal water curing, autoclaving and steam curing on the properties of a typical class-C fly ash aggregate. The 10% fines value, water absorption, and porosity of aggregates are correlated with SEM and XRD results to understand the influence of various factors and material characteristics. An increase in duration of normal water curing significantly improved the aggregate properties. Autoclaving and steam curing resulted in relatively lower enhancement in the properties as compared to normal water cured aggregate. Between the accelerated curing methods, autoclaved aggregate possessed properties closer to the normal water cured aggregate due to the dense microstructure formation. Continuation of normal water curing, after initially subjecting the aggregates to accelerated curing, exhibited only a marginal improvement in the properties.

Workability and strength behaviour of concrete with cold-bonded fly ash aggregate

This paper discusses the development of empirical models for workability and compressive strength of cold-bonded fly ash aggregate concrete in terms of mixture proportioning variables such as cement content, water content and volume fraction of cold-bonded aggregate through statistically designed experiments based on Response Surface Methodology. Factor level of cement is taken from 250 to 450 kg/m3 to introduce weak as well as strong matrix phase in the concrete. Apart from water content, workability of concrete is highly influenced by main and interaction effect of volume fraction of cold-bonded aggregate in the composition. Response surface indicate that increase in cement content causes to change the predominant failure mode from mortar failure to aggregate fracture and concrete strength decreases with increase in volume fraction of aggregate at higher cement contents. The models developed have been found useful in arriving typical relationship to establish a mixture proportioning methodology for cold-bonded fly ash aggregate concrete.

Effects of cold-bonded fly ash aggregate properties on the shrinkage cracking of lightweight concretes

Abstract This paper presents an experimental study on the restrained shrinkage cracking of the lightweight concretes made with cold-bonded fly ash lightweight aggregates. Two types of fly ash having different physical and chemical properties were utilized in the production of lightweight aggregates with different strengths. Afterwards, lower strength aggregates were also surface treated by water glass and cement–silica fume slurry to improve physical and mechanical properties of the particles. Therefore, a total of eight concrete mixtures were designed and cast at 0.35 and 0.55 water–cement ratios using four types of lightweight coarse aggregates differing in their surface texture, density, water absorption, and strength. Ring type specimens were used for restrained shrinkage cracking test. Free shrinkage, creep, weight loss, compressive and splitting tensile strengths, and modulus of elasticity of the concretes were also investigated. Results indicated that improvement in the lightweight aggregate properties extended the cracking time of the concretes resulting in finer cracks associated with the lower free shrinkage. Moreover, there was a marked increase in the compressive and splitting tensile strengths, and the modulus of elasticity.

Shrinkage cracking of lightweight concrete made with cold-bonded fly ash aggregates

Shrinkage cracking performance of lightweight concrete (LWC) has been investigated experimentally on ring-type specimens. LWCs with and without silica fume were produced at water–cementitious material ratios (w/cm) of 0.32 to 0.55 with cold-bonded fly ash coarse aggregates and natural sand. Coarse aggregate volume ratios were 30%, 45%, and 60% of the total aggregate volume in the mixtures. A total of 12 lightweight aggregate concrete mixtures was cast and tested for compressive strength, static elastic modulus, split-tensile strength, free shrinkage, weight loss, creep, and restrained shrinkage. It was found that the crack opening on ring specimens was wider than 2 mm for all concretes. Free shrinkage, weight loss, and maximum crack width increased, while compressive and split-tensile strengths, static elastic modulus, and specific creep decreased with increasing coarse aggregate content. The use of silica fume improved the mechanical properties but negatively affected the shrinkage performance of LWCs. Shrinkage cracking performance of LWCs was significantly poorer than normal weight concrete (NWC).