Cold Bonded Fly Ash Lightweight Research Articles

Thermal analysis and phase formation of eco-friendly cold-bonded high-calcium fly ash–calcium hydroxide lightweight aggregate at various curing time

The research on fly ash lightweight aggregate has been of great interest recently due to its potential for use as a substitute for natural aggregate in concrete mixes. In this work, thermogravimetric analysis of cold-bonded high-calcium fly ash lightweight aggregate with and without minor use of calcium hydroxide was investigated. Calcium hydroxide was used at 5 and 10% to replace part of fly ash. Thermogravimetric analysis measurements were carried out on samples at 0, 3 and 28 days. The results showed that calcium silicate hydrate phase in fly ash–calcium hydroxide mix is higher than reference fly ash mix. This is due to the reaction of calcium hydroxide which helps accelerate the pozzolanic reaction of fly ash. Calcium silicate hydrate was also shown to increase with curing time. Moreover, calcium hydroxide and minor calcium carbonate peaks can also be seen in all mixes while the highest amount of calcium hydroxide was found in the 90FA10CH mix.

Phase characterizations, physical properties and strength of environment-friendly cold-bonded fly ash lightweight aggregates

Natural aggregates are non-renewable resources used in excess of 40,000 Mt annually to produce concrete. Artificial aggregates from industrial by-products can be produced as environmentally friendly alternatives. The cold bonding method to produce aggregates uses much less energy compared to the sintering method. This paper reports the results of an experimental investigation on phase characterizations, physical properties and strength of environment-friendly cold-bonded fly ash lightweight aggregates. High calcium fly ash was used as the lightweight material, whereas Portland cement or calcium hydroxide was added as the binder with a small amount in the range of 5–15% by weight to produce lightweight aggregates. Increased density and enhanced crushing strength with low water absorption were found in the fly ash aggregates with the addition of Portland cement or calcium hydroxide. This is due to the occurrence of both hydration and pozzolanic reaction when compared with the fly ash mix. Furthermore, the thermogravimetry results indicate that calcium silicate hydrate, calcium hydroxide, and calcium carbonate phases were observed in all the mixes, while ettringite was also present in fly ash lightweight aggregates incorporated with Portland cement mixes. In this research study, the optimum content of Portland cement and calcium hydroxide were observed to be 10% and 5% by weight respectively. The highest crushing strength was obtained from fly ash lightweight aggregates incorporated with Portland cement at 10% by weight.

Self-Consolidating Concretes Made with Cold-Bonded Fly Ash Lightweight Aggregates

Self-Consolidating Concretes Made with Cold-Bonded Fly Ash Lightweight Aggregates

Physico-mechanical properties of self-compacting concrete containing treated cold-bonded fly ash lightweight aggregates and SiO2 nano-particles

In this experimental study, the physico-mechanical properties of self-compacting lightweight aggregate concrete (SCLC) containing artificial lightweight aggregate (LWA) made from fly ash (FA) through cold-bonded process are investigated. Coarse LWAs were treated with a soluble solution of sodium silicates (WG) in order to enhance quality. However, the binary and ternary use of fly ash (FA) and silicon dioxide nanoparticles (nS) were considered in the production of SCLC. For this, a total of 18 SCLC mixtures were designed at three different w/b ratios of 0.25, 0.37 and 0.50, and total binder contents of 600, 550 and 450kg/m3, respectively. The physical properties were tested for water sorptivity, gas permeability and water permeability, as well as for drying shrinkage. The use of treated instead of untreated LWA reduces the negative effect of w/b ratio increment of the drying shrinkage of SCLCs. The results showed that using 5.0% nano-silica and treated aggregate decreased the drying shrinkage as much as 23%. However, a significant reduction in SCLC permeability was achieved by including nS and/or treated LWAs, specifically, a reduction of up to 70% for gas permeability at 90days. Moreover, a lower compressive strength resulted due to the use of untreated aggregate and higher w/b ratio. As a general result, it was determined that a better performance is revealed at 90days for SCLCs containing 5% nS and treated LWAs, regardless of w/b ratio.

Fracture behavior and mechanical properties of concrete with artificial lightweight aggregate and steel fiber

In this study, the mechanical and fracture properties of steel fiber (SF) reinforced cold bonded fly ash lightweight aggregate concretes (LWACs) were experimentally investigated. The LWACs were produced with constant water-to-cement ratio of 0.40 and two different volume fractions of lightweight coarse aggregates (LWCA). Three types of hooked-end SFs with aspect ratios of 55, 65, and 80 were utilized 0.35%, 0.70%, 1.00%, and 1.50% of concrete volume. Effectiveness of aspect ratio, SF volume fraction, and LWCA content on the compressive, splitting, and flexural strengths as well as the modulus of elasticity, fracture energy and characteristic length of the concrete were investigated at the end of 28-days of water curing. Test results revealed that the utilization of SF crucially enhanced the splitting tensile and flexural strengths, fracture energy and characteristic length. The compressive strength, however, were not affected considerably by SF addition. Moreover, the concrete properties mentioned above were significantly influenced by artificial fly ash LWCA content.

Strength and permeability properties of self-compacting concrete with cold bonded fly ash lightweight aggregate

This paper presents the results of an experimental study on the hardened characteristics of the self-compacting concretes made with cold bond fly ash lightweight aggregates. Binary and ternary use of fly ash (FA) and silica fume (SF) blends have been considered in the production of self-compacting cold bonded fly ash lightweight aggregate concretes (SCLWCs). For this, a total of 9 SCLWC mixtures were proportioned having constant water–binder ratio of 0.35 and the total binder content of 550kg/m3. The control mixture contained only Portland cement (PC) as the binder while the remaining mixtures having binary and ternary blends of PC, FA, and SF. Properties that include compressive strength and ultrasonic pulse velocity, chloride ion penetration, gas permeability, water absorption by total immersion and by capillary absorption were investigated at two curing ages of 28 and 56days. Test results have showed that incorporating the mineral admixtures enhanced significantly the permeability characteristics. Moreover, it was observed that the compressive strength of the SCLWCs with SF was much higher than those of the control concrete.

Utilization of cold bonded fly ash lightweight fine aggregates as a partial substitution of natural fine aggregate in self-compacting mortars

In this study, lightweight fly ash fine aggregates (LWFAs) were used as a partial replacement of natural fine aggregate to investigate the fresh and hardened states of self-compacting mortars (SCMs). For this, a powder mixture of 90% fly ash (FA) and 10% Portland cement (PC) by weight were pelletized in a tilted pan through a cold-bonded agglomeration process. Thereafter, a total of five mixtures of SCMs were prepared in which natural fine aggregate was replaced by LWFA partially started from 0% to 100% by 25% increment. Subsequently, tests carried out on the fresh mortar involved mini-slump flow, mini-V-funnel flow time and viscosity while the hardened properties of SCMs were evaluated using the compressive strength, ultrasonic pulse velocity, gas permeability and sorptivity tests. The hardened characteristics of SCMs were determined at different ages up to 56days. It was observed that the increased percentage of LWFA improved the workability and the flowability of SCMs. On the other hand, the strength and permeability properties of SCMs had a negative effect due to the substitution of LWFAs for natural fine aggregate, especially at higher replacement level.

Cold Bonded Fly Ash Lightweight Aggregate Containing Different Binders

The potential applications of artificial aggregate in light weight concrete construction and prefabricated concrete elements are on the huge demand. This study investigates the production of alkali activated flyash aggregate containing different types of binders such as metakaolin, furnace slag and bentonite. The lightweight aggregate properties are greatly altered with the addition of binder material which can result in good binding properties to the flyash aggregate. The production of activated fly ash aggregate depends on the type and dosage of binders in the pelletizer. Pelletization process depends on the efficiency of production, gradation and crushing strength of aggregates which depends on the type and percentage of binder used, angle of disc, speed of disc and duration of pellet formation. The fly ash aggregates were produced and the effects of various binder materials (furnace slag (GGBS), bentonite and metakaolin) substituted at 10, 20 and 30% respectively of total binder material for various time duration were studied. The effect of alkali activator (sodium hydroxide) at a concentration of 8, 10 and 12 M, respectively were studied in flyash aggregates and the aggregates were cured in the hot air oven at 100oC up to 7 days. Test results also exhibited that water absorption flyash aggregates made using GGBS binder was found to be lower than (12.88%) compared to bentonite (16.39%) and metakaolin (17.86%). The crushing strength test results showed that a maximum strength of 22.81 MPa was obtained in the case of fly ash-furnace slag aggregate, 17.62 MPa for fly ash-metakaolin aggregate and 14.51 MPa for fly ash-Bentonite aggregate.

Effect of steel fiber addition and aspect ratio on bond strength of cold-bonded fly ash lightweight aggregate concretes

In this study, the adherence between reinforcing steel bar and the cold bonded fly ash lightweight aggregate concretes (LWAC) with and without steel fiber were evaluated by means of bond strength test. The concretes dealt with this study were produced by two different cold bonding fly ash lightweight coarse aggregate contents. The LWAC with constant water-to-cement ratio of 0.4 and 400kg/m3 cement content were designed. Three types of hooked-end steel fibers with the aspect ratios of 55, 65, and 80 were utilized with four different volume fractions of 0.35%, 0.70%, 1.00%, and 1.50% of concrete volume. The effectiveness of aspect ratio, steel fiber volume fraction, and lightweight aggregate content on the bond strength were investigated at the end of 28-days of water curing. Analyses of variance on the experimental data were performed and the levels of the significance of the lightweight aggregate content, steel fiber aspect ratio and volume fraction on the bond strength of the concretes were evaluated through general linear model analysis of variance (GLM-ANOVA). Furthermore, a mathematical model was proposed for predicting the bond strength of the concretes dealt with the current study. The results revealed that utilization of steel fiber enhanced the bond strength and the ductility of pull-out failure. Moreover, the bond strength was significantly affected by the artificial fly ash lightweight aggregate content.

Fresh properties of self-compacting cold bonded fly ash lightweight aggregate concrete with different mineral admixtures

This paper presents the results of an experimental study on the fresh properties of the self-compacting lightweight concretes made with cold bond fly ash (FA) lightweight aggregates. Binary and ternary use of FA and silica fume (SF) blends have been investigated in the production of self-compacting cold bonded FA lightweight aggregate concretes (SCLWCs). A total of 9 SCLWC mixtures were proportioned having constant water-binder ratio of 0.35 and the total binder content of 550 kg/m3. The control mixture contained only Portland cement (PC) as the binder while the remaining mixtures incorporated binary and ternary blends of PC, FA, and SF. After mixing, the fresh properties of the SCLWC were tested for T500 slump flow time, slump-flow diameter, V-funnel flow time and L-box height ratio. The fresh properties of SCLWCs with and without mineral admixtures were also evaluated by statistical technique, namely GLM-ANOVA. The results indicated that the combination use of FA and SF together decreased the slump flow time and V-funnel flow time. L-box height ratio, on the other hand, improved significantly.

Durability of lightweight concretes with lightweight fly ash aggregates

This paper presents the effects of aggregate properties such as strength, porosity, water absorption, bulk density and specific gravity on the strength and durability of lightweight fly ash aggregate concrete (LWAC). The influence of properties of four aggregates (sintered lightweight fly ash aggregates, cold-bonded lightweight fly ash aggregate and normalweight aggregate) on mechanical and durability properties of concrete is discussed. Experimental results revealed that durable high-strength air-entrained lightweight concretes could be produced using sintered or cold-bonded lightweight fly ash aggregates, having comparable performance with the normalweight concretes. The use of lightweight aggregates (LWA) instead of normalweight aggregates in concrete production decreased the strength and stiffness due to the higher porosity and lower strength of the aggregate included in the concrete. However, permeability of sintered fly ash aggregate lightweight concretes was comparable and slightly lower than normalweight concrete whereas permeability of cold-bonded fly ash lightweight concrete was greater than the others. All concretes had a durability factor greater than 85, which met the requirements by showing quite perfect resistance to freeze–thaw.

Effects of fly ash properties on characteristics of cold-bonded fly ash lightweight aggregates

The study presented herein provides a new insight into the effects of physical and chemical properties of the fly ash on the characteristics of the cold-bonded fly ash lightweight aggregates. LWAs were manufactured through the cold-bonding pelletization of two fly ashes differing in their physical and chemical properties. Moreover, one type of the LWAs was surface treated by water glass. The produced fly ash aggregates were then examined by means of ESEM micrograph, EDX spectrum, and XRD pattern to resolve the microstructural and the mineralogical characteristics of the LWAs. The findings of the study revealed that the fly ash with higher specific surface and with lower CaO content yielded higher strength LWAs. Furthermore, the surface treatment with water glass provided a marked increase in the aggregate strength and a reduction in the water absorption. The LWCs made with such LWAs had a compressive strength of as high as 60 MPa.

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.