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.     

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.     

Use of natural zeolite as a supplementary cementitious material

Natural zeolite, a type of frame-structured hydrated aluminosilicate mineral, is used abundantly as a type of natural pozzolanic material in some regions of the world. In this work, the effectiveness of a locally quarried zeolite in enhancing mechanical and durability properties of concrete is evaluated and is also compared with other pozzolanic admixtures. The experimental tests included three parts: In the first part, the pozzolanic reactivity of natural zeolite and silica fume were examined by a thermogravimetric method. In this case, the results indicated that natural zeolite was not as reactive as silica fume but it showed a good pozzolanic reactivity. In the second part, zeolite and silica fume were substituted for cement in different proportions in concrete mixtures, and several physical and durability tests of concrete were performed. These experimental tests included slump, compressive strength, water absorption, oxygen permeability, chloride diffusion, and electrical resistivity of concrete. Based on these results, the performance of concretes containing different contents of zeolite improved and even were comparable to or better than that of concretes prepared with silica fume replacements in some cases. Finally, a comparative study on effect of zeolite and fly ash on limiting ASR expansion of mortar was performed according to ASTM C 1260 and ASTM C 1567. Expansion tests on mortar prisms showed that zeolite is as effective as fly ash to prevent deleterious expansion due to ASR.     

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.     

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.     

Decoupling the physical and chemical effects of supplementary cementitious materials on strength and permeability: A multi-level approach

Supplementary cementitious materials (SCMs) represent an alternative for the industry to achieve sustainability by reducing cement contents without significant compromises of the mechanical properties and enhancing durability. SCMs play a dual role during hydration: a physical effect promoting nucleation and cement hydration and a chemical effect through pozzolanic activity. Rice husk ash (RHA) and natural pozzolans (NP) were evaluated using compressive strength and durability tests in a multi-level experimental program. RHA increased the strength more than NP, which is well explained by its prominent chemical effect (78%) assessed by isothermal calorimetry and its high amorphous silica content. Both RHA and NP produced significant reductions in the permeability of the concrete, which is mostly explained by the chemical effect. Decoupling the physical and chemical effects of a SCM allows for optimisation of its manufacturing process.     

The combined benefits of CPF and RHA in improving the durability of concrete structures

The work presented is a laboratory study of controlled permeability formwork (CPF) applied to concrete where cement was partially replaced (10%, 15% and 20%) with Portuguese rice husk ash (RHA). Portuguese rice husk is a by-product which may be incinerated industrially. Various tests were carried out to evaluate the durability of concrete made with RHA at 10%, 15% and 20% replacement of cement by weight and cast with both the usual formwork and CPF. Tests carried out so far, reported in this paper, concern strength, absorption by capillarity and chloride ion penetration. Results lead to the conclusion that CPF enhances concrete performance even further when using partial cement replacement by RHA.     

The fluid transport properties of HCWA–DSF hybrid supplementary binder mortar

It has been demonstrated in several past studies that high calcium wood ash (HCWA) can be effectively used in combination with densified silica fume (DSF) as supplementary binder material to enhance the mechanical performance of concrete. The experimental investigation was conducted to study the effect of the inclusion of HCWA and DSF on the durability properties of high strength cement mortar produced. A total of twelve different mix designs of mortar were fabricated with the use of HCWA at various cement replacement levels of 0–20% in combination with 7.5% densified silica fume (DSF) and subjected to various durability tests. The durability assessments performed include tests on water absorption, air permeability, porosity and degree of carbonation. A significantly lower degree of water absorption, porosity and carbonation was observed for cement mortars with HCWA contents of 2–8% used in combination with 7.5% DSF by weight of binder as compared to an equivalent pure cement mortar.     

Influence of a fine glass powder on the durability characteristics of concrete and its comparison to fly ash

A detailed investigation carried out to ascertain the durability characteristics of fine glass powder modified concretes is reported in this paper. Tests were designed to facilitate comparisons between concretes modified with either glass powder or fly ash at the same cement replacement level. The optimal replacement level of cement by glass powder is determined from strength and hydration tests as 10%. The later age compressive strengths of glass powder and fly ash modified concretes are seen to differ by only 5%. The durability characteristics are ascertained using tests for rapid chloride permeability, alkali–silica reactivity, and moisture transport parameters. The chloride penetrability values indicate some amount of pore refinement. The potential of glass powder to reduce the expansion due to alkali–silica reaction is established from tests conducted in accordance with ASTM C 1260, but fly ash is found to perform better at similar replacement levels. Glass powder–fly ash blends that make up a 20% cement replacement level are found to be as efficient as 20% fly ash in reducing expansion. The control concrete is seen to exhibit the lowest overall moisture intake after 14 days of curing, and fly ash concrete the highest, with the glass powder concrete in between. The trend is reversed at later ages, demonstrating that both the replacement materials contribute to improved durability characteristics. The sorptivity and moisture diffusion coefficient values calculated from the moisture intake-time data also demonstrate a similar trend. These studies show that fine glass powder has the potential to improve the durability of concretes.     

Effect of metakaolin and silica fume on the durability of self-consolidating concrete

Metakaolin (MK) is a valuable admixture for concrete/cement applications that can enhance the performance of cementitious composites through high pozzolanic reactivity, much like silica fume (SF). While SF concrete is characterized by superior mechanical and durability performance, concrete containing MK achieves comparable properties at a lower price and with better workability. The objective of this study is to investigate the effect of cement replacement by MK on the durability of self-consolidating concrete (SCC); the effect of SF at similar levels of MK replacement has also been included for comparison. The durability performance of SCC was evaluated based on the results of drying shrinkage, freezing and thawing, salt scaling, and rapid chloride permeability tests. The results of these tests indicate that highly durable SCC mixtures can be produced using a high MK content with an optimum percentage of around 20%. The results also show that the durability of SCC, especially with high MK content, is higher than that of SCC containing SF.     

Effect of rice-husk ash on durability of cementitious materials

In this paper the effects of partial replacements of Portland cement by rice-husk ash (RHA) on the durability of conventional and high performance cementitious materials are investigated. Different percentages of RHA replacement levels, two RHAs (amorphous and partially crystalline optimized by dry-milling) and several water–cementitious materials ratio are studied. The following durability aspects were tested: air permeability, chloride ion penetration, alkali-silica expansion, sulfate and acid resistance. The results were compared with those of cementitious materials without RHA. It is concluded from the tested properties that the incorporation of both RHAs in concretes show different behaviors for air permeability and chloride ion penetration depending on the water/cementitious materials ratio used; in mortars, it reduces the mass loss of specimens exposed to hydrochloric acid solution and decreases the expansion due to sulfate attack and the alkali-silica reaction. The results of durability aspects due to physical or pozzolanic effects after the addition of both RHAs, and its chemical composition, in general indicate an enhanced performance, proving the feasibility of its rational utilization as a supplementary cementing material.     

The use of oil shale ash in Portland cement concrete

An experimental investigation was undertaken to study the potential use of Jordanian oil shale ash (OSA) as a raw material or an additive to Portland cement mortar and concrete. Different series of mortar and concrete mixtures were prepared at different water to binder ratios, and different OSA replacements of cement and/or sand. The compressive strength of mortar and concrete specimens, cured in water at 23 °C, was determined over different curing periods which ranged from 3 to 90 days. The results of these tests were subjected to a statistical analysis. Equations were developed by regression analysis techniques to relate the effect of batch constituents on the strength developments of OSA mortars and concretes. The models were checked for accuracy by comparing their predictions with actual test results.The obtained results indicated that OSA replacement of cement, sand or both by about 10% (by wt) would yield the optimum compressive strength, and that its replacement of cement by up to 30% would not reduce its compressive strength, significantly. It was found that OSA on its own possesses a limited cementitious value and that its contribution to mortar or concrete comes through its involvement in the pozzolanic reactions. The statistical model developed showed an excellent predictability of the compressive strength for mortar and concrete mixes.     

Chloride induced corrosion of reinforcement in volcanic ash and pumice based blended concrete

This paper reports the results of experiments evaluating the corrosion resistance of plain, volcanic ash (VA) and volcanic pumice powder (VPP) concrete mixes. Variables were VA and VPP additions of 0–20% as cement replacement and cement contents. X-ray diffraction (XRD) analysis, electrochemical and electromechanical measurements and physical tests were used to monitor the corrosive behaviour of embedded steel bars in concretes. Results showed that additions of VA and VPP are effective in inhibiting corrosion of reinforcing bars. The superior performance in inhibiting corrosion in reinforcing steel is attributable to the densification of the cement-paste matrix due to pozzolanic action in the VA and VPP concrete mixes.     

Portland cement-fly ash-silica fume systems in concrete

Laboratory flow, strength, and ultrasnic pulse velocity tests were performed on mortars made with 70% (by weight) of portland cement and 30% of pozzolanic materials where the pozzolanic materials consisted of various combinations of fly ash and silica fume. In addition to these ternary systems, binary blends, such as Portland cement and fly ash, and Portland cement and silica fume, along with 100% Portland cement mortars, were investigated for comparison. The purpose of the investigation, preliminary in nature, was to see under what circumstances, if any, would be a synergistic action when a ternary system of Portland cement-fly ash-silica fume is used in a mortar or concrete.Mortars were made with two cements of type I and two cements of type III along with class F and class C fly ashes. One silica fume was used. Standard flow tests were performed on the fresh mortars, and compressive strength as well as ultrasonic pulse velocity tests were performed with each hardened mortar at various ages up to 28 days. It is expected that the results and conclusions obtained here on mortars will be transferable to concretes.There are several novel, or at least lesser known, results of the investigation. For instance, a new explanation is offered for the plasticizing effect of fly ash which is based on the optimum particle-size distribution concept. Another such result is that ground fly ash produced greater flow increases with type I cement than with type III. A third finding is that the superplasticizer is more effective in increasing the flow as well as strength when the mortars contain fly ash and/or silica fume than in the case of mortars without mineral admixture. Also, it appears that when type I cement is used, the silica fume in the quantity of 5% of the weight of the cement produces relatively greater strength increase in the presence of fly ash than without fly ash.These promising results are preliminary in nature. Therefore, further research is justified with ternary systems in concrete. The presented work is a portion of a larger investigation.     

Effect of ground fly ash and ground bagasse ash on the durability of recycled aggregate concrete

This research aims to study the effect of ground fly ash (GFA) and ground bagasse ash (GBA) on the durability of recycled aggregate concrete. Recycled aggregate concrete was produced with recycled aggregate to fully replace crushed limestone in the mix proportion of conventional concrete (CON) and GFA and GBA were used to partially replace Portland cement type I at the rate of 20%, 35%, and 50% by weight of binder. Compressive strength, water permeability, chloride penetration depth, and expansion by sulfate attack on concretes were investigated.The results reveal that the use of GFA and GBA to partially replace cement in recycled aggregate concrete was highly effective in improving the durability of recycled aggregate concrete. The suitable replacement of GFA or GBA in recycled aggregate concrete to obtain the suitable compressive strength, low water permeability, high chloride penetration resistance, and high sulfate resistance is 20% by weight of binder.     

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.     

Porosity and water permeability of rice husk ash-blended cement composites reinforced with bamboo pulp

Cellulose fibres have already been applied commercially as an alternative to asbestos in fibre-cements composites. In spite of their industrial scale production for more than 20 years, these composites still require much research efforts, which focus mainly on durability aspects. The influence of the most relevant deterioration mechanisms can be minimized if mineral admixtures with high pozzolanic activity replace ordinary Portland cement (OPC). The improvements then achieved are due to the decrease in Ca(OH)₂ content and the more compact matrix and interfaces in the composite. In this respect, rice husk ash (RHA) is one of the most promising materials to be applied as a partial cement replacement in the cellulose-reinforced cement-based composites. This is due to the high active silica content of the ash and the widespread availability of the husks. To assess the influences of different chemical compositions of RHA, and the effects of autoclave curing on the pore characteristics of bamboo-pulp-reinforced cement composites, a comparative study was carried out in which pore characteristics were assessed by mercury intrusion porosimetry (MIP). Complementarily, the effects exerted by changes in the pore structure of the composites on their water permeability are evaluated by analytical and experimental approaches. It was observed that the incorporation of RHA in the composites could cause an extensive pore refinement in the matrix and in the interface layer, thereby decreasing water permeability. The results indicate that partial replacement of cement by RHA can improve the durability characteristics of cellulose–cement composites.     

Assessing the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste

This study assesses the effect of biomass ashes with different finenesses on the compressive strength of blended cement paste. rice husk ash (RHA), palm oil fuel ash (POFA) and river sand (RS) were ground to obtain two finenesses: one was the same size as the cement, and the other was smaller than the cement. Type I Portland cement was replaced by RHA, POFA and RS at 0%, 10%, 20%, 30% and 40% by weight of binder. A water to binder ratio (W/B) of 0.35 was used for all blended cement paste mixes. The percentages of amorphous materials and the compressive strength of the pastes due to the hydration reaction, filler effect and pozzolanic reaction were investigated. The results showed that ground rice husk ash and ground palm oil fuel ash were composed of amorphous silica material. The compressive strength of the pastes due to the hydration reaction decreased with decreasing cement content. The compressive strength of the pastes due to the filler effect increased with increasing cement replacement. The compressive strengths of the pastes due to the pozzolanic reaction were nonlinear and were fit with nonlinear isotherms that increased with increasing fineness of RHA and POFA, cement replacement rate and age of the paste. In addition, the model that was proposed to predict the percentage compressive strength of the blended cement pastes on the basis of the age of the paste and the percentage replacement with biomass ash was in good agreement with the experimental results. The optimum replacement level of rice husk ash and palm oil fuel ash in pastes was 30% by weight of binder; this replacement percentage resulted in good compressive strengths.     

Compressive strength and durability properties of ceramic wastes based concrete

This paper presents an experimental study on the properties and on the durability of concrete containing ceramic wastes. Several concrete mixes possessing a target mean compressive strength of 30 MPa were prepared with 20% cement replacement by ceramic powder (W/B = 0.6). A concrete mix with ceramic sand and granite aggregates were also prepared as well as a concrete mix with natural sand and coarse ceramic aggregates (W/B = 0.5). The mechanical and durability performance of ceramic waste based concrete are assessed by means of mechanical tests, water performance, permeability, chloride diffusion and also accelerated aging tests. Results show that concrete with partial cement replacement by ceramic powder although it has minor strength loss possess increase durability performance. Results also shows that concrete mixtures with ceramic aggregates perform better than the control concrete mixtures concerning compressive strength, capillarity water absorption, oxygen permeability and chloride diffusion. The replacement of cement and aggregates in concrete by ceramic wastes will have major environmental benefits.     

Effect of pozzolans on the performance of fiber-reinforced mortars

Randomly oriented short fibers have been shown to increase tensile strength and retard crack propagation of cement based materials such as fiber-reinforced mortars for diverse applications, especially in aggressive environments. In the case of reinforced concrete, it is very important to produce a “high quality” cover in order to prevent corrosion of the rebars. In order to obtain a high performance material the use of a pozzolan is advisable because low permeability is achieved. The objective of this research was to determine the effect of pozzolans such as silica fume (SF), fly ash (FA), and metakaolin (MK) on the properties of fiber-reinforced mortars. Different types of natural and synthetic fibers were used. A superplasticizer was used to keep the same workability as that of the control mortar. Results of the mechanical and durability properties of the fiber-reinforced mortars are reported. The results show that a loss of resistance due to embedding fibers in mortar is compensated for by the increase in strength caused by silica fume or metakaolin additions to the mortar. The addition of 15% of SF or MK produces an improvement of up to 20% and 68%, respectively, when compared with those mortars without addition. There is a significant decrease in the coefficient of capillary absorption and chloride penetration when a highly pozzolanic material is incorporated into the matrix. In general, these materials, especially SF and MK, improve the mechanical performance and the durability of fiber-reinforced materials, especially those reinforced with steel, glass or sisal fibers. The fly ash addition had a different performance, which could be attributed to its low degree of pozzolanicity.