Effect of W/B ratios on pozzolanic reaction of biomass ashes in Portland cement matrix

In this study, the effects of W/B ratios on pozzolanic reaction of by-product biomass ashes, namely rice husk-bark ash (RHBA) and palm oil fuel ash (POFA), were determined. These biomass ashes were ground to the same fineness as that of Type I Portland cement (OPC) and partially replaced OPC at replacement levels of 10-40% by weight of binder. Water to binder (W/B) ratios of 0.50, 0.575, and 0.65 were used. The compressive strengths of mortars were compared to those of mortars made with OPC partially replaced with ground river sand of similar particle size. The results demonstrate that at the same cement replacement levels, the degrees of pozzolanic reaction of RHBA and POFA increase with W/B ratio. In addition, ground river sand with the same particle size of OPC can be used as a non-reactive material to replace OPC for determining the compressive strength due to pozzolanic reaction of biomass ash.     

Strength,drying shrinkage,and water permeability of concrete incorporating ground palm oil fuel ash

In this study, palm oil fuel ash (POFA) was used as a pozzolanic material in concrete. The POFA was ground to obtain two different finenesses: coarse (CP) and fine (FP). A portion of ordinary type I Portland cement (OPC) was replaced by CP and FP at 10%, 20%, and 30% by weight of binder to cast concrete. Compressive strength, modulus of elasticity, drying shrinkage, and water permeability of concretes containing ground POFA were measured. The results showed that the compressive strength of the concrete increased with the fineness of the POFA. With 10% and 30% replacement of OPC by CP and FP, respectively, the compressive strength of the resulting concrete was as high as that of OPC concrete at 90 days. Moreover, the use of 10–30% of FP as a cement replacement in concrete reduced its drying shrinkage and water permeability. Finally, there was also a strong correlation between the compressive strength and the water permeability of ground POFA concrete.     

Particle size effect on the strength of rice husk ash blended gap-graded Portland cement concrete

Rice husk ash (RHA) has been used as a highly reactive pozzolanic material to improve the microstructure of the interfacial transition zone (ITZ) between the cement paste and the aggregate in high-performance concrete. Mechanical experiments of RHA blended Portland cement concretes revealed that in addition to the pozzolanic reactivity of RHA (chemical aspect), the particle grading (physical aspect) of cement and RHA mixtures also exerted significant influences on the blending efficiency. The relative strength increase (relative to the concrete made with plain cement, expressed in %) is higher for coarser cement. The gap-grading phenomenon is expected to be the underlying mechanism. This issue is also approached by computer simulation. A stereological spacing parameter (i.e., mean free spacing between mixture particles) is associated with the global strength of the blended model cement concretes. This paper presents results of a combined mechanical and computer simulation study on the effects of particle size ranges involved in RHA-blended Portland cement on compressive strength of gap-graded concrete in the high strength/high performance range. The simulation results demonstrate that the favourable results for coarser cement (i.e., the gap-graded binder) reflect improved particle packing structure accompanied by a decrease in porosity and particularly in particle spacing.     

Effect of utilizing unground and ground normal and black rice husk ash on the mechanical and durability properties of high-strength concrete

The aim of the present study is to investigate the effects of utilizing different processings of normal rice husk ash (RHA) and black rice husk ash (BRHA) on the mechanical and durability properties of high-strength concrete (HSC). Mechanical and durability properties of HSC were evaluated on concrete mixes containing unground BRHA and RHA and ground BRHA and RHA, their average particles sizes being 165, 85, 67 and 24 µm, respectively. The replacement of ordinary Portland cement with the ashes was adopted at 20%. The results showed that incorporating any form of RHA and BRHA in HSC reduced the slump value. The surface areas of RHA and BRHA, not their carbon content, determined the dosage of superplasticizer needed to achieve a targeted slump value. Concrete with unground and ground RHA incorporated exhibited 30% higher compressive strength while unground BRHA produced 30% lower compressive strength than that of the control concrete. Incorporating unground and ground RHA showed a synergy between filler and pozzolanic effect and had insignificant difference in mechanical and durability properties of the concretes. Meanwhile, incorporating ground BRHA showed a dominant filler effect in the concrete. Overall, the improvement of splitting tensile strength and modulus of elasticity of both RHA and GBRHA concrete showed a similar trend to that of the compressive strength of RHA concrete. The durability of concretes with unground and ground RHA and ground BRHA incorporated showed better performance than that of the control concrete. The material with 20% ground BRHA as partial cement replacement in HSC of Grade 50 could be used without any reduction in the mechanical and durability properties. Use of unground BRHA is not recommended because it did not improve these properties.     

Effect of grinding of low-carbon rice husk ash on the microstructure and performance properties of blended cement concrete

The effectiveness of unground low-carbon rice husk ash (URHA) as a pozzolan and the effect of grinding the URHA to finer fractions for use in portland cement system were investigated. The properties investigated include the setting time and calcium hydroxide depletion of rice husk ash (RHA) pastes; microstructure and flow behavior of RHA mortars; strength and durability of RHA concretes. Results from this investigation suggested that the URHA and ground RHA (GRHA) mixtures performed better than the control mixtures in all tests conducted except water demand and setting time. The URHA mixture revealed denser microstructure compared to the control mixture. The internal porosity created by the coarse RHA grains in the matrix and their inability to completely participate in pozzolanic reaction may be the reasons for the poorer performance of the URHA mixture than compared to the GRHA mixture. The effect of grinding the RHA to finer fractions either substantially or slightly improved all properties except final setting time. With the performance of the GRHA concrete somewhat similar to that of the SF concrete, the use of ground RHA can be concluded to provide acceptable performance in portland cement systems.     

Physical and pozzolanic action of mineral additions on the mechanical strength of high-performance concrete

Pozzolans play an important role when added to Portland cement because they usually increase the mechanical strength and durability of concrete structures. The most important effects in the cementitious paste microstructure are changes in pore structure produced by the reduction in the grain size caused by the pozzolanic reactions pozzolanic effect (PE) and the obstruction of pores and voids by the action of the finer grains (physical or filler effect). Few published investigations quantify these two effects. Twelve concrete mixtures were tested in this study: one with Portland cement (control), nine mixtures with 12.5%, 25% and 50% of replacement of cement by fly ash, rice husk ash and limestone filler; two with (12.5+12.5)% and (25+25)% of fly ash and rice husk ash. All the mixtures were prepared with water/binder ratios of 0.35, 0.50, and 0.65. The compressive strength for the samples was calculated in MPa per kg of cement. The remaining contents of calcium hydroxide and combined water were also tested. The results show that the pozzolanic and physical effects have increased as the mineral addition increased in the mixture, being higher after 91 days than after 28 days. When the results for the same strength values are compared (35 and 65 MPa), it was observed that the filler effect (FE) increased more than the pozzolanic effect. The PE was stronger in the binary and ternary mixtures prepared with rice husk ash in proportions of 25% or higher.     

Pozzolanicity of finely ground lightweight aggregates

This paper examines the pozzolanic behavior of finely ground lightweight aggregates with a mean particle size between 4 and 26 μm. Cement pastes are made with a 20% mass replacement of cement with finely ground lightweight aggregates, fly ash, quartz, and limestone in addition to a control paste with no cement replacement. Isothermal calorimetry, thermogravimetric analysis, and compressive strength testing as well as thermodynamic calculations are performed on these pastes. Isothermal calorimetry and compressive strength testing are shown to not be able to clearly distinguish and quantify the pozzolanic response of the finely ground lightweight aggregates, fly ash, quartz, and limestone when they are used in cement pastes. However, thermogravimetric analysis and thermodynamic calculations clearly show that the finely ground lightweight aggregates are pozzolanic through the consumption of calcium hydroxide. A pozzolanic reactivity test based on isothermal calorimetry also confirms that the finely ground lightweight aggregates are pozzolanic. These results indicate that finely ground lightweight aggregates are pozzolanic and could be used in concreting applications.     

Influence of 15 and 80 nano-SiO2 particles addition on mechanical and physical properties of ternary blended concrete incorporating rice husk ash

This study demonstrates the effects of SiO₂ nanoparticles as additives with two different sizes of 15 and 80?nm on compressive strength and porosity of rice husk ash (RHA) blended concrete. Up to 20% of ordinary Portland cement (OPC) was replaced by RHA with average particle size of 5 micron. Also, SiO₂ nanoparticles were added to the above mixture at four different weight percentages of 0.5, 1.0, 1.5 and 2.0 and cured in lime solution. The results indicated that compressive strength of Portland cement–nano SiO₂–rice husk ash (PC–NS–RHA) ternary blended concrete was considerably increased. Moreover, the total amount of porosity decreased to a minimum with respect to the control concrete. This improvement was observed at all the curing ages and replacement levels, but there was a gain in the optimal point with 20% of RHA plus 2% of 80?nm SiO₂ particles at 90 days of curing.     

Effect of fly ash fineness on compressive strength and pore size of blended cement paste

This paper presents an experimental investigation on the effect of fly ash fineness on compressive strength, porosity, and pore size distribution of hardened cement pastes. Class F fly ash with two fineness, an original fly ash and a classified fly ash, with median particle size of 19.1 and 6.4 μm respectively were used to partially replace portland cement at 0%, 20%, and 40% by weight. The water to binder ratio (w/b) of 0.35 was used for all the blended cement paste mixes.Test results indicated that the blended cement paste with classified fly ash produced paste with higher compressive strength than that with original fly ash. The porosity and pore size of blended cement paste was significantly affected by the replacement of fly ash and its fineness. The replacement of portland cement by original fly ash increased the porosity but decreased the average pore size of the paste. The measured gel porosity (5.7–10 nm) increased with an increase in the fly ash content. The incorporation of classified fly ash decreased the porosity and average pore size of the paste as compared to that with ordinary fly ash. The total porosity and capillary pores decreased while the gel pore increased as a result of the addition of finer fly ash at all replacement levels.     

Use of rice husk ash in sandcrete blocks for masonry units

Different mix proportions of sand, cement and rice husk ash (RHA) were studied for use in sandcrete blocks. Optimum water/(cement+RHA) ratios were determined at different mix proportions. Compressive strengths of various mix proportions at 7, 28 and 60 days were also determined. The optimum water/(cement+RHA) ratio increased with rice husk ash contents. Test results showed that up to 40% RHA could be added as a partial replacement for cement without any significant change in compressive strength at 60 days. Compressive strengths of various mix proportions were compared with British Statutory minimum compressive strengths of bricks for various walls and it was found that sandcrete blocks of 1∶5 mortar mixes with 40% RHA (by weight of cement) could be used in both load and non-load bearing walls.     

Influence of treated palm oil fuel ash on compressive properties and chloride resistance of engineered cementitious composites

The influence of palm oil fuel ash (POFA) inclusion on the compressive properties and chloride resistance of engineered cementitious composites (ECC) were experimentally investigated. In the material development, pozzolanic reactivity of POFA, direct tensile test and matrix fracture test were performed for evaluating the performance of ECC with POFA. Different ECC mixes with varying POFA content and water–binder ratios were used. The results show that the use of POFA should be helpful for achieving strain-hardening behavior by enhancing the fracture toughness and interfacial bond between matrix and PVA fiber. Moreover, at 28 and 90 days, increasing the POFA/cement ratio up to 0.2 led to an increase in the compressive strength of the ECC. The ECC mix with 1.2 POFA–cement ratio achieved a compressive strength of 30 MPa at 28 days, which is within the normal range of concrete strength for many applications. In addition, the test results show that mechanically pre-loaded POFA–ECC specimens exposed to chloride solution remain durable. The results also indicated strong evidence of self-healing of micro-cracked POFA–ECC specimens, which can still carry considerable flexural load. The rapid chloride permeability test reveal that the total charge passed was gradually reduced with the inclusion of higher amount of POFA. The results presented in this study provide a preliminary database for the durability of cracked and uncracked POFA–ECCs under chloride environment or/and combined mechanical loading.     

Evaluation of bagasse ash as supplementary cementitious material

The utilization of waste materials in concrete manufacture provides a satisfactory solution to some of the environmental concerns and problems associated with waste management. Agro wastes such as rice husk ash, wheat straw ash, hazel nutshell and sugarcane bagasse ash are used as pozzolanic materials for the development of blended cements. Few studies have been reported on the use of bagasse ash (BA) as partial cement replacement material in respect of cement mortars. In this study, the effects of BA content as partial replacement of cement on physical and mechanical properties of hardened concrete are reported. The properties of concrete investigated include compressive strength, splitting tensile strength, water absorption, permeability characteristics, chloride diffusion and resistance to chloride ion penetration. The test results indicate that BA is an effective mineral admixture, with 20% as optimal replacement ratio of cement.     

The hydration properties of pastes containing municipal solid waste incinerator fly ash slag

This study investigated the hydration properties of Type I, Type III and Type V cements, mixed with municipal solid waste incinerator fly ash, to produce slag-blended cement pastes. The setting time of slag-blended cement pastes that contained 40% slag showed significantly retardation the setting time compared to those with a 10% or even a 20% slag replacement. The compressive strength of slag-blended cement paste samples containing 10 and 20% of slag, varied from 95 to 110% that developed by the plain cement pastes at later stages. An increased blend ratio, due to the filling of pores by C-S-H formed during pozzolanic reaction tended to become more pronounced with time. This resulting densification and enhanced later strength was caused by the shifting of the gel pores. It was found that the degree of hydration was slow in early stages, but it increased with increasing curing time. The results indicated that it is feasible to use MSWI fly ash slag to replace up to 20% of the material with three types of ordinary Portland cement.     

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.     

Stabilization/solidification of lead-contaminated soil using cement and rice husk ash

This paper presents the findings of a study on solidification/stabilization (S/S) of lead-contaminated soil using ordinary Portland cement (OPC) and rice husk ash (RHA). The effects of varying lead concentrations (in the form of nitrates) in soil samples on the physical properties of their stabilized forms, namely unconfined compressive strength (UCS), setting times of early mixtures and changes in crystalline phases as well as chemical properties such as leachability of lead, pH and alkalinity of leachates are studied. Results have indicated that usage of OPC with RHA as an overall binder system for S/S of lead-contaminated soils is more favorable in reducing the leachability of lead from the treated samples than a binder system with standalone OPC. On the other hand, partial replacement of OPC with RHA in the binder system has reduced the UCS of solidified samples.     

Self compacting concrete from uncontrolled burning of rice husk and blended fine aggregate

This paper presents an experimental study on the development of normal strength Self compacting concrete (SCC) from uncontrolled burning of rice husk ash (RHA) as a partial replacement to cement and blended fine aggregate whilst maintaining satisfactory properties of SCC. Experiments on the fresh and hardened state properties have been carried out on RHA based SCC from uncontrolled burning. The dosages of RHA are limited to 0%, 20%, 30% and 40% by mass of the total cementitious material in the concrete. The experiments on fresh state properties investigate the filling ability, the passing ability and the segregation resistance of concrete. The experiments on hardened state properties investigate the compressive and the splitting tensile strengths. The water absorption level of the concrete with changing RHA levels has also been monitored. The experimental studies indicate that RHA based SCC developed from uncontrolled burning has a significant potential for use when normal strength is desired.     

Properties of binary and ternary blended cement mortars containing palm oil fuel ash and metakaolin

Abstract

This paper has investigated the properties of mortars made from binary and ternary blends of metakaolin (MK), palm oil fuel ash (POFA), and ordinary Portland cement (OPC). A total of 17 different mortar mixtures were produced. The OPC in the mixtures was partially replaced by MK, POFA, or a combination of MK and POFA at different replacement levels of (0–30%) by weight of the binder. At the fresh state, the flow (workability) of mortar mixtures was determined, while at the hardened state, the compressive strength and porosity at the ages of 7, 28, and 90 days were evaluated. The results showed that the flow of mortar is boosted with the combined use of MK and POFA compared to when MK is separately used. Besides, improvement in low early compressive strength development and reduction in high porosity from use of POFA occurred with the addition of up to 10% MK content. Therefore, the combination of POFA and MK could be used as a supplementary cementitious material to produce cement-based material of higher quality than OPC.     

Strength development of concrete with rice-husk ash

This paper presents a study on the development of compressive strength up to 91 days of concretes with rice-husk ash (RHA), in which residual RHA from a rice paddy milling industry in Uruguay and RHA produced by controlled incineration from the USA were used for comparison. Two different replacement percentages of cement by RHA, 10% and 20%, and three different water/cementicious material ratios (0.50, 0.40 and 0.32), were used. The results are compared with those of the concrete without RHA, with splitting tensile strength and air permeability. It is concluded that residual RHA provides a positive effect on the compressive strength at early ages, but the long term behavior of the concretes with RHA produced by controlled incineration was more significant. Results of splitting tensile and air permeability reveal the significance of the filler and pozzolanic effect for the concretes with residual RHA and RHA produced by controlled incineration.     

Water absorption control of ternary blended concrete with nano-SiO2 in presence of rice husk ash

In the current study, the effects of SiO₂ nanoparticles as additive with two different sizes of 15 and 80?nm on water absorption of rice husk ash (RHA) blended concrete have been investigated. Concrete samples were prepared by replacing 10, 15 and 20?wt% of cement with RHA and 0.5, 1.0, 1.5 and 2.0% of cement with SiO₂ nanoparticles followed by curing in lime solution for 7, 28 and 90?days. The results indicated that the resistance to water absorption of Portland cement?Cnano SiO₂?Crice husk ash (PC?CNS?CRHA) ternary blended concrete was considerably improved with respect to the control concrete. This improvement was observed at all curing ages and replacement levels but the optimal point was reached for 20% of RHA incorporating 2% of 80?nm SiO₂ particles at 90?days of curing. Fast formation of C?CS?CH gel in the presence of ultra high active nano-sized SiO₂ and micron level RHA particles together with their high filler effect may result in a continuous cement paste with the lowest weak zones. It has been concluded that the use of novel ternary blended concrete (PC?CNS?CRHA) provides significant reduction in the water absorption of concrete.     

Creep analysis of concrete containing rice husk ash

This paper presents an experimental study on the mechanical properties of concrete added with rice husk ash (RHA) as a supplementary cementitious material. The compressive strength, modulus of elasticity and creep were obtained experimentally from specimens with different RHA contents (0%, 10%, 15% and 20% of binder). The results show that the addition of RHA in concrete can improve both the compressive strength and modulus of elasticity and reduce the creep of concrete. The examination of pore micro-structure of hardened concrete using both the mercury intrusion porosimetry and scanning electron microscope techniques demonstrates that RHA particles can react with calcium hydroxide originated from cement hydration to produce additional C-S-H, which can fill voids and large pores and thus reduces the porosity related to capillary pores and voids. In addition, the release of absorbed water, which is retained in the small pores of RHA particles at early days, can improve cement hydration and thus reduce the porosity related to gel pores.