Fly Ash Concrete Mixes Research Articles

Performance of cementitious systems containing calcined clay in a chloride-rich environment: a review by TC-282 CCL

In this review by TC- 282 CCL, a comprehensive examination of various facets of chloride ingress in calcined clay-based concrete in aggressive chloride-rich environments is presented due to its significance in making reinforced concrete structures susceptible to chloride-induced corrosion damages. The review presents a summary of available literature focusing on materials characteristics influencing the chloride resistance of calcined clay-based concrete, such as different clay purity, kaolinite content and other clay minerals, underscoring the significance of pore refinement, pore solution composition, and chloride binding mechanisms. Further, the studies dealing with the performance at the concrete scale, with a particular emphasis on transport properties, curing methods, and mix design, are highlighted. Benchmarking calcined clay mixes with fly ash or slag-based concrete mixes that are widely used in aggressive chloride conditions instead of OPC is recommended. Such comparison could extend the usage of calcined clay as a performance-enhancing mineral admixture in the form of calcined clay or LC2 (limestone-calcined clay). The chloride diffusion coefficient in calcined clay concrete is reported to be significantly lower (about 5–10 times in most literature available so far) compared to OPC, and even lower compared to fly ash and slag-based concrete at early curing ages reported across recent literature made with different types of cements and concrete mixes. Limited studies dealing with reinforcement corrosion point out that calcined clay delays corrosion initiation and reduces corrosion rates despite the reduction in critical chloride threshold. Most of these results on corrosion performance are mainly from laboratory studies and warrant field evaluation in future. Finally, two case studies demonstrating the application of calcined clay-based concrete in real-world marine exposure conditions are discussed to showcase the promising potential of employing low-purity calcined clay-based concrete for reducing carbon footprint and improving durability performance in chloride exposure.

Effects of Fly Ash on Compressive Strength and Durability Properties of Lean Concrete

Concrete production and waste generation are among human activities that negatively impact the environment. This study investigated the effects of fly ash on compressive strength and durability properties of lean concrete using appropriate standard methods. The results showed that the compressive strength of the control mix is higher than those of fly ash concrete mixes. The compressive strength of the fly ash blended mixes decreased as the replacement level increased. However, the strength increased with hydration time, and the optimal replacement level being 5%. While the chloride ion penetration and water absorption rate decreased, the sulfate resistance increased with hydration time and replacement level. The fly ash mixes exhibited better durability properties than the control mix in all durability tests conducted. The SEM-EDX analysis showed that mixes with well-packed microstructures exhibited favorable compressive and durability properties. In conclusion, Class C fly ash is recommended for lean concrete mixes at a replacement level of up to 15% when compressive strength is the primary concern, while mixes with a replacement level of 25% or more are recommended in areas susceptible to sulfate attack.

GA-based hybrid ANN optimization approach for the prediction of compressive strength of high-volume fly ash concrete mixes

GA-based hybrid ANN optimization approach for the prediction of compressive strength of high-volume fly ash concrete mixes

Rebar corrosion and ASR durability assessment of fly ash concrete mixes using high contents of fine recycled aggregates

This research assessed the potential alkali silica reaction (ASR) of fine recycled aggregates (FRA) derived from precast concrete slabs using petrographic examination and expansion tests, the effects of incorporating FRA on some chloride related transport properties and the corrosion risk of fly ash blended concretes. Mixes incorporating 20 % fly ash (FA) were produced using water-to-binder ratios of 0.45 and 0.50 and FRA replacements of 0 %, 20 %, 60 % and 100 % to test concrete’s mechanical performance, chloride penetrability and rebar corrosion risk using electrochemical techniques at different ages. FRA presented an ASR expansion 227 % higher than natural aggregates. Using high contents (>60 %) of FRA didn’t increase corrosion risk and a comparable risk to conventional concrete was observed when incorporating FA.

Performance and life-cycle assessment of high-volume fly ash concrete mixes containing steel slag sand

The present study discusses the performance of high-volume fly ash concrete (HVFAC) mixes containing slag sand which is a solid waste obtained from basic oxygen steel making industry. The design of such mixes was optimized to attain sufficient strength for structural purposes and then cement and natural sand in them were replaced with fly ash and slag sand up to 50%. Other than temperature developments, their fresh and hardened properties like slump, air content, compressive and tensile strengths, elastic modulus, strain softening response under uniaxial compression, shrinkage, water permeation, sorption and absorption, chloride ions diffusion and migration, and bulk electrical resistance at different ages were also studied in detail. The impact of fly ash and slag sand on the sustainability of such mixes were assessed and their co-effects on concrete microstructure were discussed with the results of scanning electron microscopy and Mercury intrusion porosimetry. The HVFAC mixes displayed a slower strength increase at early ages, but they were found to be highly workable, durable, and temperature rise in them was comparatively lower. The strength and durability of these mixes at early ages were found to enhance in the presence of slag sand which is generally capable of strengthening the aggregate-paste interface. India is the second largest producer of cement in the world. Both the fly ash and slag sand possess a lower energy requirement and their inclusions led to the production of eco-friendly concrete which is highly desirable for Indian conditions.

The effect of silica fume on the washout resistance of environmentally friendly underwater concrete with a high-volume of siliceous fly ash

Concrete with a high-volume of siliceous fly ash has recently been widely applied as underwater concrete (UWC) in marine structures. This study investigated the effect of the content of silica fume (SF) and the source of fly ash (FA) on the washout resistance of high-volume fly ash concrete (HVFAC) mixes. Class F fly ash sourced from two different locations in India was used to prepare eight HVFAC mixes, which were stabilized using increasing SF contents of 0, 5, 10, and 15 wt%, respectively. The washout loss of these UWC mixes was determined using a special plunge test with a long acrylic washout tube and a perforated steel container. Moreover, other properties such as the slump, air content, strength, void content, water permeability and sorptivity, and drying shrinkage of the prepared mixes were also validated. An enhancement in slump and washout resistance of up to 19% and 11% were noticed when the UWC mixes were prepared using FA with a greater surface area. With an increase in the content of SF, there was also an increase in the loss of the workability and strength of the UWC mixes. Moreover, the washout resistance and durability of these mixes increased. This confirms that the inclusion of SF stabilized the HVFAC mixes against water environments by adsorbing more free water on their surfaces. The pozzolanic reaction and microstructure densification mechanisms also increased the stabilization of the HVFAC. Designing UWC using HVFAC mixes stabilized with SF is environmentally friendly, and the application of such concretes in underwater environments is simple and cost-effective.

Investigation of sulphate resistance of the nano reinforced blended concrete

In the present study, the control mix (M 30 grade), optimum blended concrete mix containing cement, vetrified tiles powder, silica fume and fly ash and blended concrete mix reinforced with Multi Walled Carbon Nano Tubes were considered and investigated the resistance offered by them against the sulphate attack. The specimens of the respective mixes were immersed in 10% Na2SO4 for a period of 180 days. The optimum blended mix obtained from the previous study contains 60% cement, 7% silica fume, 25% vetrified tiles powder and 8% fly ash. The reinforced blended mixes were developed by incorporating well dispersed Multi Walled Carbon Nano Tubes in the dosage percentages of 0.01%, 0.02%, 0.03%, 0.05% and 0.1% by weight of binder content. The resistance offered by the mixes against the sulfate attack was evaluated in terms of visual investigation, loss in weight, compressive strength and ultrasonic pulse velocity test. Mass loss was observed to vary between 0.3% and 0.7% for the blended specimens and less than 0.2% for the nano engineered blended concrete specimens at 180 days of immersion period when compared to the control mix. The microstructural investigation was carried out using SEM-EDX and XRD to determine the morphology and the formation of the crystalline phases of the matrix after immersion in the solution. From the study carried out it was observed that the reinforced blended mix containing 0.05% of the carbon nano tubes have outperformed all other mixes by exhibiting the highest resistance to the sulfate attack in terms loss of mass, compressive strength and the quality of the concrete. The mix have shown the highest compressive strength value of about 54 MPa at the end of the immersion period which is about 23% higher than the control mix. It can be concluded that the concrete developed not only reduce the carbon foot print on the environment but also contribute towards the high resistance against the sulfate attack.

GGBS: Fly-Ash evaluation and mechanical properties within high strength concrete

The behavior of concrete in the form of an adhesive made with activated silicon and aluminium in a highly alkaline solution is investigated in this study. Research on concrete based on low calcium fly ash is widely used. The fly ash with high calcium content can also be suitable as a base material for producing geopolymers. In this investigation, the exact ideal substitution amount of GGBS: Fly Ash for PPC concrete mix was determined to be 60:40. For different sodium hydroxide and sodium silicate chemical ratios in the concrete mix, different results were produced. This research adds to our understanding of the performance of various strength concretes and GGBS as partial cement substitutes. Mechanical strength and durability properties and acid attack were discovered in the GGBS and Fly Ash concrete mix. Sodium Silicate and sodium hydroxide have been discovered to affect various combinations as well as strength and durability.

Characterization of physico-chemical and functional properties of fly ash concrete mix

Ever - increasing utilization and cement requirement have forced the researchers to develop alternate building materials that have eco-friendly nature and will contribute towards less waste management. Industries and governmental agencies are looking towards waste reduction. In this paper, the effect of fly ash percentage on concrete properties is demonstrated. Present work deals with the partial replacement of cement weight by 5–20% fly ash. In the present study, M20 grade concrete and water to cement ratio of 0.5 was used. The properties like workability, water demand, heat of hydration for fresh concrete and compressive strength, permeability, durability for harden concrete were studied and compared with Fly Ash based concrete mix. The fly ash based concrete mix showed promising results from constructional point of view. Hence, from the present study, it can be concluded that Fly Ash concrete mix can be used as a partial replacement of normal concrete mix.

Impact of Silica Nanoparticles on the Durability of fly Ash Concrete

In the present study, the mechanical and durability properties of silica nanoparticle (SNP)-incorporated fly ash (FA) concrete mix were examined after 365 days of exposure. The dosages of FA replaced by cement in the present study were 30%, 40%, and 50%, while 3% SNPs were added by the weight of cement in the FA incorporated mix. For a comparison of SNPs with silica fume (SF), 6% SF was added (by the weight of cement) and entire casting was performed at a constant water to binder (w/b) ratio of 0.29. The present work is the extension of a previous study wherein durability properties of the same mixes were reported for up to 180 days of exposure. Compressive strength results show that in the presence of SNPs, the enhancement in compressive strength was in the range of 10–14%, while, in presence of SF, 8–10% of the enhancement was observed as compared to control. However, exposed samples in a carbonation environment showed that the compressive strength of the control and SF incorporated mix increased, while SNP-incorporated samples showed negligible enhancement. Further, sulphate exposed mix show that compressive strength decreases, however, the SNP-incorporated mix showed the lowest reduction compared to other mixes. Therefore, the study shows that the SNP-incorporated mix has higher mechanical properties and more durability compared to other mixes in a severe environment.

An investigation into age-dependent strength, elastic modulus and deflection of low calcium fly ash concrete for sustainable construction

In the present experimental and analytical investigation, the age-dependent effect on the compressive strength, elastic modulus, and long-term behaviour of concrete having class F fly ash have been studied. The fly ash concrete mixes were prepared by replacing the cement with fly ash in the range of 25% to 60% with equivalent weight. A total of eight different mixes of plain and fly ash concrete were prepared. The strength in compression and static elastic modulus was measured experimentally at different ages varying from 7 to 180 days on cylindrical specimens for all the mixes of concrete. The reinforced concrete (RC) beams containing fly ash of overall size of 100 × 150 × 1800 mm (B × D × L) were also cast to observe the creep and shrinkage deflection under the sustained loading of 50% stress level. The microstructure study using scanning electron microscopy along with dispersive X-Ray spectroscopy on all plain and fly ash concrete mixes have also been conducted. The concrete having 40% fly ash content shows satisfactory performance at later ages (i.e. beyond 28 days) in terms of strength, modulus of elasticity, and deflection. It has been observed that the gain in strength from 28 to 180 days is more in fly ash concrete than the plain concrete. The gain in creep and shrinkage deflection from 28 to 180 days is reduced in fly ash concrete beams. Thus, the effective use of fly ash in the concrete enhances the mechanical properties due to its pozzolanic behavior. The assessment of existing models on the prediction of compressive strength and static modulus of elasticity has been done. New models for the prediction of age-dependent compressive strength and elastic modulus of concrete containing the varying percentage of fly ash have been proposed. The present experimental and analytical study can be useful for practicing engineers and designers in the design of concrete structures containing low calcium fly ash for sustainable construction.

Experimental and analytical investigation on the age-dependent tensile strength of low-calcium fly ash-based concrete

In this study, the age-dependent splitting and flexural tensile strength have been investigated by incorporating the various percentages of fly ash in the plain concrete mixes. The partial replacement of cement by fly ash was varied from 0 to 60% on an equal weight basis. Standard concrete specimens were cast for measuring splitting and flexural tensile strength at different ages, i.e., 7, 28, 56, 90, 150, and 180 days, for all plain and fly ash concrete mixes. Experimental results show that the fly ash produced a significant effect on the tensile strength of concrete mixes. It has been observed that the fly ash concrete mixes gain considerable tensile strength with respect to age beyond 28 days. In the low-calcium fly ash concrete mixes, the rate of development of tensile strength from 28 to 180 was observed higher in comparison with the plain concrete mixes. The assessment of the existing models for the estimation of age-dependent tensile strength recommended by design codes and researchers with experiments has also been done on various mixes of plain and fly ash concrete. New models to predict the age-dependent splitting and flexural tensile strength of concrete having different percentages of fly ash are proposed. The present experimental and analytical study will be helpful for the designers and practicing engineers for fixing preliminary dimensions of reinforced and prestressed concrete members and mix proportioning of low-calcium fly ash concrete mixes.

Accuracy of maturity functions’ strength estimates for fly ash concretes cured at elevated temperatures

The effect of elevated curing temperature on the strength development of concrete mixes with fly ash (FA) has been investigated for strength grades C32/40 and C55/67. Percentages of fly ash in the total binder were 15, 30 and 45 per cent. High curing temperatures have a beneficial effect on the early age strength but a detrimental effect on the long-term strength development. Fly ash concrete mixes have been shown to be less sensitive to curing at high temperatures than Portland cement (PC) concretes and this was reflected in their lower “apparent” activation energies. The accuracy of strength estimates obtained from maturity functions was examined. The temperature dependence of the Nurse-Saul function, i.e. the concrete strength gain rate varies linearly with temperature, was not sufficient to account for the improvement in early age strengths resulting from high curing temperatures. The Arrhenius based function, on the other hand, overestimated them because of the detrimental effect of high curing temperature on strength starting from a very early age. Both functions overestimate long term strengths as neither accounts for the detrimental effect of high curing temperatures on the ultimate compressive strength.

Effect of nano-silica addition into high volume fly ash–hydrated lime blended concrete

This study investigates strength development, reactivity and environmental/economic benefits of blended High Volume Fly Ash (HVFA) concrete mixes utilizing 65% and 80% cement replacement utilizing a combination of fly ash and hydrated lime, with and without nano-silica. The carbon and non-carbon emissions are considered as environmental impacts while life cycle costs from cradle-to-gate, which is from material extraction to production, are considered for comparison of the economic benefits. The compressive strength of the HVFA mixes increased with the addition of nano-silica. The HVFA–65 and HVFA–80, without nano-silica, achieved 25.0 MPa and 14.5 MPa at 7 days, respectively, and 42.7 MPa and 29.5 MPa at 28 days. With the addition of nano-silica the HVFA–65 ns and HVFA–80 ns concrete had compressive strengths of 37.5 MPa and 28.8 MPa at 7 days and increased to 47.1 MPa and 40.1 MPa at 28 days. Incorporating 3% nano-silica into HVFA concrete increased the early age hydration reaction. This is attributed to the reaction of the C3A and C4AF phases and the formation of monosulfoaluminate, which contributed to the early age strength gain. The majority of Ca2+ ions were consumed during the initial hydration, with few Ca2+ ions remaining for the subsequent hydration reaction with the C3S phase. The HVFA concrete mixes displayed between 51 and 60 % carbon savings and a reduced Global Warming Impact. The non-Greenhouse Gas emissions, i.e. SO2 and NOx, reflects minor savings in the Acidification Impact (AI) and Photochemical Oxidant Formation Impact (POFI) environmental impact indicators. Further, HVFA concrete incorporated with hydrated lime shows a 10% cost reduction compared with Portland Cement concrete.

Non-Destructive Assessment of Heated Rc Columns Cooled by Two Cooling Methods

Fire constitutes a major hazard to the buildings. The structural members exposed to high temperatures during fire accidents. The phenomenon observed was the structural members undergo dehydration of concrete, thermal distress in the form of cracking and spalling due to excessive heating. This leads to cause degradation of concrete strength. After tackle the fire hazard, the next step is to find the suitability of the building for repair or restoration, which involves assessment of fire severity and fire damage. Nondestructive testing (NDT) is the most practical and widely used methods to obtain in place strength or even for new structure strength. It is an effective tool for damage assessment and quality assurance, as well. In this paper, reinforced concrete (RC) columns made with OPC mix and HVFA mix, exposed to high temperatures ranging from 100 to 800°C. After heating, the specimens were brought to room temperature by air cooling and water quenching methods. The specimens were tested for residual compressive strengths and material integrity of concrete columns, by non-destructive testing methods, to understand how parameters like cooling condition and exposure duration influence the mechanical properties of conventional concrete mix and fly ash concrete mix. OPC concrete mix columns performed better strengths over HVFA mix columns when they cooled by air. Whereas water quenched HVFA mix columns upkeep the concrete quality grading on comparing the OPC mix specimens.

Effect of incorporating hydrated lime on strength gain of high-volume fly ash lightweight concrete

High-volume fly ash concrete, HVFALC, may acquire popularity as durable, resource-efficient, and option of sustainability for different applications of concrete. The Pozzolanic reaction between fly ash, Ca(OH)2 and water is the cause of making high-volume fly ash concrete a promising sustainable material. The aim of this study is to enhance the rate of the Pozzolanic reaction by incorporating external source of hydrated lime in the mix by two approaches. The first is to replace 10% by weight of the cementitious materials with hydrated lime and second is to use a lime-saturated water, with a concentration of 3g/L, for mixing. Two high-volume fly ash concrete mixes, with 50 and 60 % replacement by weight of cement, were included in this study. The testing program included water absorption, dry density, compressive and splitting tensile strengths. The testing program was extended to the age of 120 days.The present results showed that both approaches have caused an increase, ranging between 10 and 24 %, in absorption values and a slight reduction, less than 3 %, in dry density values. Both approaches have caused a significant gain in compressive and splitting tensile strengths. Replacing 10 % by weight of the cementitious materials with hydrated lime caused better enhancement in compressive and splitting tensile strengths for all curing ages than using lime-saturated water in mixing. The former approach was more effective for mix FA60 than for FA50 and the higher fly ash content in the FA60 mixes could be the reason.

Optimization of fly ash concrete mix – a solution for sustainable development

This paper presents a method for optimizing fly ash concrete mix using the data obtained through planned experimental program.The full factorial experimental technique involving three factors with their four levels (4x4x4) were used. A total of 64 mixes with three replicates (192 specimens) were cast by taking three parameters for optimization. The three parameters were water to binder ratio (0.4, 0.45, 0.5, 0.55); coarse aggregate to total aggregate ratio (0.5, 0.55, 0.6, 0.65) and four percentages of fly ash i.e. 0%, 25%, 40% & 60%. The cement density used in the experimental program were 400 kg/m3. These parameters were taken in such a way that the various combinations of these factors would yield optimum concrete mix in the practical range of compressive strength. Two grades of concrete i.e. M20 and M30 were obtained from experimental investigation. The experimental data were utilized to develop the regression model for compressive strength in terms of three design factors considered in this study. The test results showed that optimum compressive strength was achieved at 0.45 water to binder ratio and 0.6 coarse aggregate to total aggregate ratio at 25% replacement of cement with fly ash.

Rheological and strength properties of self-compacting concrete incorporating marble and granite powders

The use of waste products like fly ash in self-compacting concrete (SCC) is a common practice. In regions where a lot of waste generated due to sawing and polishing of granite and marble has a huge potential of using them in concrete without compromising the rheology and strength. This paper presents the experimental investigations on rheological behavior (T500, Vft, and viscosity) and strength properties (compressive, flexural, and splitting tensile strengths) of SCC made of marble and granite powders. The comparison was made with higher fly ash and higher sand content concrete mixes. The rheological properties showed similar and linear inter-relationship between different sets of mixes. Most of the mixes fall under VS2/VF1 and VS2/VF2 categories of EFNARC specifications. The strength properties of SCC mixes were compared with normal concrete mixes and found analogues with control concrete mix. The use of marble and granite powders up to 360 kg/m3 was studied. There is a beneficial effect due to the reduction of other raw materials significantly in concrete mixes. The admixture dosage was identified and found to be dependent on the surface area of particles.

Accelerated Carbonation Assessment of High-Volume Fly Ash Concrete

The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation depth appeared to decrease with increase in compressive strength, but this correlation was not significant.

Optimization and Development of High-Strength High-Volume Fly Ash Concrete Mixes

Cement is the most abundantly used ingredient in the production of concrete due to which its production and use has increased manifold. To reduce the carbon footprint left by the cement production, fly ash is used as cement replacement in concrete. Past research studies suggest that the fly ash replacement can be upto 40% beyond which there will be drastic reduction of strength. In the present study, high strength concrete mix of 70 grade is developed with high volume fly ash of 70% as cement replacement. Silica fume of 10% and hydraulic lime of 30% are used as additives in the development of M70 grade high-strength high-volume fly ash concrete. In the present paper, three types of fly ashes are considered for the study of which one which is ultrafine is chosen based on the pozzolanic index and strength activity index. Excess lime needed for various percentage of fly ashes is evaluated based on the empirical equationsgiven by the Dunstan Jr andZayed.