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.     

Influence of fly ash blending on hydration and physical behavior of belite–alite–ye’elimite cements

A cement powder, composed of belite, alite and ye’elimite, was blended with 0, 15 and 30 wt% of fly ash and the resulting blended cements were further characterized. During hydration, the presence of fly ash caused the partial inhibition of both AFt degradation and belite reactivity, even after 180 days. The compressive strength of the corresponding mortars increased by increasing the fly ash content (68, 73 and 82 MPa for mortars with 0, 15 and 30 wt% of fly ash, respectively, at 180 curing days), mainly due to the diminishing porosity and pore size values. Although pozzolanic reaction has not been directly proved there are indirect evidences.     

Mineralogical and microstructural characterization of biomass ash binder

While the incineration of biomass residues is gaining traction as a globally available source of renewable energy, the resulting ash is often landfilled, resulting in the disposal of what could otherwise be used in value-added products. This research focuses on the beneficial use of predominantly rice husk and sugarcane bagasse-based mixed biomass ashes, obtained from two paper mills in northern India. A cementitious binder was formulated from biomass ash, clay, and hydrated lime (70:20:10 by mass, respectively) using 2M NaOH solution at a liquid-to-solid mass ratio of 0.40. Compressive strength of the biomass ash binder increased linearly with compaction pressure, indicating the role of packing density. Between the two mixed biomass ashes used in this study, the one with higher amorphous content resulted in a binder with higher strength and denser reaction product. Multi-faceted characterization of the biomass ash binder indicated the presence of aluminum-substituted calcium silicate hydrate, mainly derived from the pozzolanic reaction.     

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.     

Thermal activation on calcium silicate slag from high-alumina fly ash: a technical report

The fly ash with alumina composition from 45 to 55 % has been found in China in last 10 years, which attracts great attention from Chinese government and related alumina industry. Chinese government and its state-owned enterprises have successfully extracted the Al as alloy product from the high-alumina fly ash. However, to recycle the calcium silicate slag as residue from the Al industry is still undetermined. In this report, an innovative process is introduced to achieve the regional sustainability for the high-alumina fly ash industry, and it is found that the cementitious material composed of calcium silicate slag met with the mechanical requirements of 32.5 cement for road pavement. The chemical and mineral analysis show that the calcium silicate slag has high CaO content, which reaches up to 48.64 %. C₂S and C₃A are the dominant mineral phases by XRD analysis indicating its potential pozzolanic activity during the hydration process. Thermal activation from 200 to 900 °C was applied to enhance its pozzolanic activity for the calcium silicate slag and it proved that 600 °C is the optimal calcination temperature due to the decomposition of calcite and clay minerals. Also the mineral phase amorphization was also observed during the XRD analysis, which might also contribute to the enhanced pozzolanic properties at 600 °C. Although the designed cementitious material contains a large quantity of solid waste, none of the hazardous heavy metals exceed the EPA limits. This short article originally reported a promising direction for managing solid waste for Al industry and enhancing utilization efficiency for the enterprise internal solid wastes.     

Pozzolanic activity of palm bunch wastes

The paper reports an investigation of the ash from the burnt stalks of oil palm bunches as a suspected agricultural waste with pozzolanic activity. Chemical analysis confirmed the presence of the major elements silica, alumina, potassium and a comparatively low content of calcium, all of which are necessary for pozzolanic activity. Limestone, shale, lead and sodium carbonates were independently mixed with the ash to improve the pozzolanic activity, which was low without the introduction of these conditioners. It was confirmed that limestone together with lead carbonate are good additives that can enhance pozzolanic activity in the ash. The ash was therefore classified as a pozzolana which can be used to produce pozzo-lime cement or used as a blender with ordinary Portland cement.     

Evidence of the influence of the cationic composition on the anionic affinity of layered double hydroxides

The effect of the cationic composition on the anionic affinity is evaluated by studying the reconstruction of the layered double hydroxide structure from mixed oxides obtained by the heat treatment of the Mg₄Al₂-layered double hydroxides solid solution, in aqueous solutions containing carbonates, sulfates, and nitrates. After synthesis, all the samples present the same c parameter whatever the iron content. After a thermal treatment at moderate temperature, amorphous mixed oxides are obtained from all the samples. The influence of the cationic composition is clearly demonstrated on the anionic affinity as the Mg₄Al₂-amorphous mixed oxides reconstructs the layered double hydroxide structure with 90 % carbonates and 10 % sulfates whereas the Mg₄Fe₂-amorphous mixed oxides reconstruct the layered double hydroxide structure with 89 % carbonates, 7 % sulfates, and 4 % nitrates. The nitrate ratio increases as the iron content increases.     

DSC and TG Analysis of a Blended Binder Based on Waste Ceramic Powder and Portland Cement

Cement industry belongs to the business sectors characteristic by high energy consumption and high \(\hbox {CO}_{2}\) generation. Therefore, any replacement of cement in concrete by waste materials can lead to immediate environmental benefits. In this paper, a possible use of waste ceramic powder in blended binders is studied. At first, the chemical composition of Portland cement and ceramic powder is analyzed using the X-ray fluorescence method. Then, thermal and mechanical characterization of hydrated blended binders containing up to 24 % ceramic is carried out within the time period of 2 days to 28 days. The differential scanning calorimetry and thermogravimetry measurements are performed in the temperature range of \(25\,^{\circ }\hbox {C}\) to \(1000\,^{\circ }\hbox {C}\) in an argon atmosphere. The measurement of compressive strength is done according to the European standards for cement mortars. The thermal analysis results in the identification of temperature and quantification of enthalpy and mass changes related to the liberation of physically bound water, calcium-silicate-hydrates dehydration and portlandite, vaterite and calcite decomposition. The portlandite content is found to decrease with time for all blends which provides the evidence of the pozzolanic activity of ceramic powder even within the limited monitoring time of 28 days. Taking into account the favorable results obtained in the measurement of compressive strength, it can be concluded that the applied waste ceramic powder can be successfully used as a supplementary cementing material to Portland cement in an amount of up to 24 mass%.     

Hydration of high-volume fly ash cement pastes

The hydration processes of high-volume fly ash cement paste were investigated by examining the non-evaporable water content, the CH content, the pH of pore solution and the fraction of reacted fly ash, curing at either 20°C or elevated temperatures after an initial curing at 20°C. The replacement percentage levels of fly ash were 40%, 50% and 60% by weight, respectively. The results revealed that the non-evaporable water content in high-volume fly ash cement pastes does not develop as plain cement pastes does, so it may be improper to apply the non-evaporable water content to evaluate the hydration process in high-volume fly ash cement matrix. The reduction in CH content increases with the progressing of hydration process and varies linearly with the logarithm of curing age. The addition of 3.0% of Na₂SO₄ could accelerate the pozzolanic reaction of fly ash at early ages. At 20°C, the pH of pore solution of high-volume fly ash cement paste was reduced to a great extent at early ages and it continued to decline at later ages due to the inclusion of large amount of fly ashes. At elevated temperatures, however, this trend was not found. The fraction of reacted fly ash directly reflects the pozzolanic reactivity of fly ash both at normal and elevated temperatures. There is some inherent correlation between the reduction in CH content, the pH of pore solution and the fraction of reacted fly ash. For specified matrix, the consumption of CH and the pH of pore solutions change linearly with the increase of the fraction of reacted fly ash.     

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.     

Application of thermally activated municipal solid waste incineration (MSWI) bottom ash fines as binder substitute

Untreated municipal solid waste incineration (MSWI) bottom ash fines (0–2 mm) have poor pozzolanic properties, and contain substances which can pose an environmental risk (e.g. heavy metals and salts). This study investigates combined treatments applied on bottom ash fines (BAF) to increase their reactivity. The treated BAF is compared with both untreated BAF and cement, and its contribution to cement hydration is investigated. Additionally, the utilization of the treated BAF in mortar as cement replacement is tested. Finally, the leaching properties of mortars containing treated and untreated BAF are estimated. According to the results obtained, the 28-day compressive and flexural strengths of mortar with 30% treated bottom ash are about 16% and 6% lower than the reference mortar, respectively. The leaching of contaminants from the crushed mortars with BAF are well under the limit values imposed by Dutch legislation.     

Performance and energy calculation on a green cementitious material composed of coal refuse

Coal refuse as industrial solid waste has become great threats to the environment. To activate coal refuse is one practical solution to recycle this huge amount of solid waste as substitute for ordinary Portland cement (OPC). Compared with conventional cement production, successful development of this new material could potentially save energy and reduce greenhouse gas emissions, recycle vast amount of coal wastes, and significantly reduce production cost. Coal refuse was confirmed as a pozzolanic material, which enhances its durability performance. In this experiment, 60 % of the OPC was substituted with the pozzolana mixture (30 % coal refuse + 25 % slag + 5 % FGD gypsum), which is an optimal solution for the creation of good-performance cementitious material. Compared with OPC, the 60 % pozzolana blended sample has a much higher resistance to the alkali-silica reaction and Cl ion penetration. In addition, microanalyses of the activated coal refuse by XRD demonstrated that some of the mineral phase changes in coal refuse were related to the performance of the cementitious material. For example, the transformation of kaolinite into metakaolin and the dehydroxylation of muscovite enhance the resistance of the cementitious material to the alkali-silica reaction and Cl penetration, respectively. Compared with conventional cement production by calculation, successful development of a new thermal activation process (800 °C) to convert coal refuse into desirable pozzolanic material for producing the new material would potentially save energy around by about 50 %, reduce greenhouse gas emissions by about 67 %.     

Hydrophobic and water-resisting behavior of Portland cement incorporated by oleic acid modified fly ash

The water-repellent and anti-permeability properties of cement are crucial for the durability and safety of concrete structures. In this work, we prepared a hydrophobic Portland cement by using oleic acid as a modifier for fly ash and examined the properties of the cement paste samples. Fly ash was firstly reacted with oleic acid by the dry milling method, and the modified fly ash was used to prepare the hydrophobic Portland cement. The IR spectra confirmed that the surface of fly ash was successfully capped with oleic acid, and carboxylic acid moieties were bonded with ≡SiOH and neutralized. The TG-DSC results showed that the amount of oleic acid loaded on the fly ash beads was 7.21 wt%. Fly ash dispersed evenly in the prepared cement paste samples and the distance between beads ranged in 2–10 μm. The water contact angle of the cement paste samples increased with rising content of modified fly ash, which demonstrated good water-repellent behavior. Different cement sections showed similar water-repellent behavior, which proved that the inner structure of the cement was also hydrophobic. Using the fly ash modified with oleic acid significantly decreased the water uptake and gas permeability of the prepared cement paste samples. The hydrophobic cement sample was optimal when the content of the modified fly ash in the cement was 12 wt% and after the cement was cured for 28 days.     

Comparing the mechanical properties of cold recycled mixture containing coal waste additive and ordinary Portland cement

Pavement cold recycling is considered as an efficient rehabilitation method, especially in severely distressed roads. Modifier additives have been used for improving the performance of cold recycled mixture (CRM), especially at initial days of curing. In this study, coal waste taken from coal washing plant and its ash produced through the incineration process were used as pozzolanic additives in CRM with bitumen emulsion. To assess the effects of using these additives on mechanical properties of CRM, Marshall stability, indirect tensile strength (ITS), resilient modulus, dynamic creep and fatigue tests were applied. Furthermore, the effect of using these additives on CRM moisture sensitivity was evaluated. Application of coal waste powder improved the mechanical properties of CRM, but it could not exert a positive effect on CRM moisture sensitivity. Thus, coal waste can be used as CRM additive in conditions that moisture damage does not significantly affect the pavement performance. Unlike the coal waste powder using the coal waste ash not only increased the durability of CRM, but also it showed upgrading the mechanical properties. In continue, the mechanical properties of the CRM containing coal waste and its ash were compared with the mix that stabilised with 1% and 2% ordinary Portland cement (OPC). Based on the comparisons, coal waste powder and its ash had comparable effects to OPC. For example, the results of fatigue tests revealed that at higher strain levels of 200 μ? the fatigue life of the CRM mix containing 7% coal waste and coal waste ash was higher than that of containing 1% and 2% cement. Finally, apart from the several environmental advantages it was concluded that the use of coal waste powder and its ash had technical benefits in cold recycling with bitumen emulsion.     

Effect of aged binder on piezoelectric properties of cement-based piezoelectric composites

Age-dependent piezoelectric properties of cement piezoelectric composites containing cement-based binder and 50 vol. % PZT piezoelectric inclusions are conducted. The effect of binder with 10 to 50 % cement replaced by slag and fly ash is investigated. Specimens are polarized by 1.5 kV/mm for 30 min when the curing time reaches 7, 28 and 56 days, respectively. Experimental values are measured daily till 120 days after the polarization. Prior to polarization, dielectric loss needs to be less than 0.73 to guarantee the feasibility of polarization. Piezoelectric properties including d ₃₃, g ₃₃ and ?_r are age-dependent unless the age is higher than 60 days after the polarization. The electromechanical coupling coefficient κ_t is independent of the ages. The curing time shows less efficient to piezoelectric properties while hydration reaction is completed. 20 vol. % cement replaced by slag or fly ash provides optimum d ₃₃ and g _33. Compared with slag replacement, fly ash replacement can diminish ?_r, but increase κ_t. In addition, a modified equation to calculate the dielectric constant of PZT/cement composites is also proposed.     

Comportement pseudo-pouzzolanique d'une cendre volante de centrale thermique

Résumé Les auteurs étudient le comportement d'une cendre voltante riche en sulfates et ne libérant pas de silice, en vue de préciser le r?le des sulfates dans le caractère pouzzolanique. A cette fin, ils comparent les résistances mécaniques de mortiers riches en cendre volante à celles de mortiers témoins, suivent leur hydratation par examen aux rayons X et analysent l'activité de la cendre placée au contact d'eau pure et d'eau de chaux saturée. La cohésion initiale des mortiers de cendre s'accro?t par formation de sulfoaluminates jusqu'à environ un mois. Par la suite, l'absence de réaction pouzzolanique empêche la progression des propriétés mécaniques des mortiers et enlève tout intérêt pratique à ce type de cendre.

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Summary In earlier work we have shown that pozzolanic properties of some fly ashes used in Portland cement concretes result of two distinct reactions: first, fly ashes release sulphates which combine with calcium hydroxyde and calcium aluminate to form ettringite; then, silica passes into solution and reacts with lime to produce C.S.H. To define the effect of sulphates, we have undertaken the present study with another ash having a low soluble silica content. Cristalline components are the major constituent, some 60 %, and consist chiefly of quartz (35 %), magnetic (15 %), hematite (5 %) anhydrite (3 %). The specific surface value is 5200 cm²/g (Blaine). We have made four type of 1:3 sand mortars with Portland cement (CPA 400) and quartz aggregate having a maximum size of3.15 mm. In the first, cement only was used (w/c ratio of0.50). Second and third mortars contained equal volumes of cement and fly ash and w/(cement+fly ash)=0.50; fly ash added to the third mortar had been previously washed in water to eliminate soluble sulphates. A fourth mortar was made with equal volumes of cement and finely ground quartz. Initially, sulphates brought by fly ash make easy ettringite formation in mortars: X-ray examination show that the content of ettringite in raw fly ash mortars, is, at 2 days, twice more important that in washed fly ash ones. The main effect of this reaction is to increase strength of mortars of about40 to45%. Then, during the first month of hardening, calcium sulphoaluminate goes on forming in mortars; but the high-sulphate form is converted to low-sulphate. This last reaction starts at about seven days and is probably due to sodium and magnesium sulphates released by fly ash. During this first month strength of mortars continues to increase. At longer age, calcium sulphoadluminate formation is stopped and ettringite goes on converting to low sulphate form and tetracalcium aluminate. Fly ash does not release silica able to combine with calcium hydroxyde: therefore strength of mortars does not increase with age.

     

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.     

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.     

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.     

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.