Utilization of copper tailing for autoclaved sand–lime brick

The influences of the batch ingredients and the autoclaving processes on the properties of autoclaved sand–lime brick from low SiO₂ content copper tailing were studied. The results show that the copper tailing with low content of SiO₂ can be used to produce autoclaved sand–lime bricks meeting GB11945-1999 for Mu 15 sand–lime brick, if only the proportion of the copper tailing in the brick batch does not exceed 50% (% by mass) and appropriate proportions of river sand and sand powder are added to compensate for the low SiO₂ content. XRD and SEM analyses show that the main hydrothermal reaction products in the brick are 0.9 nm, 1.1 nm and 1.4 nm tobermorite phases, and the andradite in the copper tailing nearly does not take part in the autoclaving reaction.     

Preparation of load-bearing building materials from autoclaved phosphogypsum

Previous studies have been carried out on calcined phosphogypsum (PG) for making the building materials. The present study was focused on autoclaved PG and its use in making load-bearing wall bricks. Autoclaved PG was prepared from original waste PG with steam pre-treatment. The crystalline phase, morphology, and thermal characteristics of original waste PG and autoclaved PG were investigated by XRD, SEM, and SDT. Then bricks of the size of Chinese standard brick were prepared from different types of PG in the PG-fly ash–lime–sand system. Results showed that the compressive strength of bricks from autoclaved PG by lower-pressure steam of 0.12 MPa, 120 °C for 16 h was much higher. The flexural strength and compressive strength of the bricks could reach 4.0 MPa and 15.0 MPa, respectively. The durability of the bricks was investigated by 15 freezing–thawing cycles at temperatures from ?20 °C to 20 °C, and the weight loss was only 0.029% after all of cycles. Hemihydrates (CaSO₄ · 0.5H₂O) were dehydrated products from dihydrates in original PG with lower-pressure steam treatment, and hemihydrates were susceptible to absorbing the humidity and were transformed into densified re-crystallization gypsum (CaSO₄ · 2H₂O) that contributed to the final strength of bricks. Microstructural characteristics of bricks were investigated by XRD and SEM. Tobermorite was the significant hydrated product, which contributed to the strength of bricks. The use of autoclaved PG for making load-bearing wall bricks was recommended instead of conventional burnt clay bricks.     

Fly ash addition in clayey materials to improve the quality of solid bricks

The technical quality of two compositionally different groups of solid bricks fired between 800 and 1000 °C was evaluated. Five weight percentage of fly ash was added to both groups and they were compared with similar bricks with no added fly ash.The textures of the bricks with fly ash were very similar to the textures of those without it, except that the samples with the additive contained spherical fly ash particles with diameters ranging from 0.1 to 10 μm. These particles led to a reduction in the density of the bricks and a substantial improvement in their durability, with less decay being caused by salt crystallization in the pores. This is because fly ash causes a reduction in the number of micropores, the pores that make porous materials most vulnerable to salt-induced decay. Use of this additive could have practical implications as a means of recycling and for achieving cost savings in brick production.     

Autoclaved brick from low-silicon tailings

The load-bearing brick is made from low-silicon tailings by pressing and autoclaving process, in the presence of alkali-activated slag/fly ash cementing material (AAFSC). Tailings accounts for 83% of the total mass of the brick. The compressive strength of the brick is up to 16.1 MPa, bending strength 3.8 MPa, and with low drying shrinkage and good freeze–thaw resistance. Some factors influencing the mechanical strength of the brick including forming pressure, forming water content and curing regime, are investigated. The hydration products, freeze–thaw durability and anti-carbonation characteristics of the products are discussed.     

Development of alpha plaster from phosphogypsum for cementitious binders

Efforts have been made to make high strength alpha plaster from phosphogypsum, a by-product of phosphoric acid industry. Phosphogypsum was autoclaved in slurry form (phosphogypsum 50% + water 50%, by wt.) in the laboratory at different steam pressures for different durations in presence of chemical admixtures. It was found that with small quantity of chemical admixture (sodium succinate/potassium citrate/sodium sulphate), alpha plaster of high strength can be produced. The optimum pressure and duration of autoclaving was found to be as 35 psi and 2.0 h, respectively. The alpha plaster was examined for making cementitious binders by admixing hydrated lime, fly ash, granulated blast furnace slag, marble dust and chemical additives with alpha plaster. Data showed that cementitious binder of compressive strength of 22.0 and 30 MPa (at 28 days of curing at 40° and 50 °C) and low water absorption was produced. DTA and SEM studies of the binder showed formation of CSH, ettringite and C₄AH₁₃ as main cementitious products to give strength.     

Influence of fly ash on strength and sorption characteristics of cold-bonded fly ash aggregate concrete

Cold-bonded fly ash aggregate concrete with fly ash as part of binder or fine aggregate facilitates high volume utilization of fly ash in concrete with minimum energy consumption. This paper investigates the influence of fly ash on strength and sorption behaviour of cold-bonded fly ash aggregate concrete due to partial replacement of cement and also as replacement material for sand. While cement replacement must be restricted based on the compressive strength requirement at desired age, replacement of sand with fly ash appears to be advantageous from early days onwards with higher enhancement in strength and higher utilization of fly ash in mixes of lower cement content. Microstructure of concrete was examined under BSEI mode. Replacement of sand with fly ash is effective in reducing water absorption and sorptivity attributable to the densification of both matrix and matrix–aggregate interfacial bond. Cold-bonded fly ash aggregate concrete with a cement content of 250 kg/m³, results in compressive strength of about 45 MPa, with a total inclusion of around 0.6 m³ of fly ash in unit volume of concrete.     

Preparation of eco-friendly construction bricks from hematite tailings

With the objective of reducing the negative impacts on environment and utilizing the secondary resource of tailings, the possibility of making construction bricks by using the hematite tailings from western Hubei province of China was investigated. Besides hematite tailings, the additives of clay and fly ash were added to the raw materials to improve the brick quality. Through the process of mixing, forming, drying and firing, the bricks were produced. The optimum conditions were found to be that the hematite tailings content were as high as 84%, forming water content and forming pressure were respectively in the range of 12.5–15% and 20–25 MPa, and the suitable firing temperature was ranged from 980 to 1030 °C for 2 h. Under these conditions, the mechanical strength and water absorption of the reddish fired specimens were 20.03–22.92 MPa and 16.54–17.93%, respectively, and the other physical properties and durability were well conformed to Chinese Fired Common Bricks Standard (GB/T5101-2003). The phases and morphologies of the green tailings and fired specimen were characterized by XRD and SEM. The results showed that the main mineral phases of the product were hematite, quartz, anorthite and tridymite, which were principally responsible for the mechanical strength of bricks.     

Preparation and characterisation of fly ash based geopolymer mortars

Geopolymer mortars with varying levels of sand aggregate were prepared and their physical and mechanical properties studied. The geopolymer binder to sand aggregate weight ratio was varied from 9 to 1. Compressive strength and Young’s modulus of the fly ash based geopolymer paste were 60 MPa and 2.27 GPa and these values did not change significantly with addition of up to 50 wt.% sand aggregate. Geopolymer binder exhibited strong bonding to the sand aggregate. Increasing sand content without increasing the amount of alkaline activator resulted in a decreasing level of geopolymerisation within the binder system.     

Durability of masonry systems: A laboratory study

We deal with the textural aspects, porometry and hydric behaviour of combinations of building materials and their durability under attack by salt crystallisation and freezing. We selected 4 types of lime mortar (pure lime mortar, lime mortar + air-entraining agent, lime mortar + pozzolana and lime mortar + air-entraining agent + pozzolana) which were used in combination with either brick or calcarenite stone. Lime mortars were chosen because they are compatible with traditional building materials, including the bricks and calcarenites that were widely used in the historical buildings that make up our architectural heritage. There are more similarities between the pore size ranges in calcarenites and mortars than there are between those in bricks and mortars. In all cases, a fine layer of calcite microcrystals develops at the contact surface between the mortar and the stone or brick. This is produced by the transformation of the portlandite, which concentrates in this area due to capillary moisture migration. This surface may on the one hand represent an obstacle to the flow of water between the different parts of the system formed by these materials, but on the other it may also favour greater adherence between the components, especially in the calcarenite + mortar combination, which proved to be the most resistant to deterioration in the freeze–thaw tests.     

Effect of fly ash addition on the mechanical properties of tile adhesive

Statistical relationship between various strengths of tile adhesives in which cement or sand was partially replaced with fly ash was studied. A low-lime fly ash was used in five different replacement levels from 5% to 30% by weight of either cement or sand. The tensile adhesion, flexural and compressive strengths of adhesives were determined at 2, 7 and 28 days. In small substitution levels, sand replacement increased the tensile adhesion strength. No strong relationship was found between tensile adhesion strength and flexural or compressive strength of the specimens in which the fly ash was used as sand replacement (r < 0.659). Strong relationship was observed between the same properties when fly ash was used as cement replacement (r > 0.896). Flexural and compressive strength values showed quite strong relationship (r > 0.949). This may be due to the fact that both of these strength values were obtained on the same specimens.     

Properties of fly ash concrete modified with hydrated lime and silica fume

This paper presents the results of an experimental investigation on the properties of fly ash concrete incorporating either hydrated lime or silica fume to improve the early strength of concrete. Test results indicated that the addition of lime and silica fume improved the early age compressive strength of fly ash concrete. The inclusion of silica fume was also found to increase the 28 days strength significantly. The air permeability of concrete containing lime and silica fume either decreased or remained almost the same when compared to the concrete without these. The addition of lime and silica fume also improved the sorptivity of concrete.Through the use of differential scanning calorimetry and thermogravimetric analysis (DSC/TG), it was demonstrated that the addition of hydrated lime increased the Ca(OH)₂ content; whereas the addition of silica fume decreased the Ca(OH)₂ content in the cement paste. The mercury intrusion porosimetry (MIP) data confirmed the beneficial action of hydrated lime and silica fume, towards decreasing the total pore volume of fly ash cement paste.     

Effects of post-mercury-control fly ash on fresh and hardened concrete properties

Activated carbon injection is the most mature technology for mercury capture from coal burning power plants; however, this technology increases the carbon content and mercury concentration in the fly ash. This, in turn, may reduce the suitability of fly ash for use in concrete and call into question the safety of using fly ash derived from this process. The focus of this paper is to investigate the reuse potential of post-mercury-control fly ash in concrete by examining the influence of three fly ashes derived from the activated carbon injection on the air content, compressive strength, permeability, and resistance to freezing and thawing of concrete mixtures. Laboratory testing confirmed the influence of the carbon on the air content of the concrete. However there was no difficulty in entraining air in activated carbon injection fly ash concretes within the recommended dosage range of the air-entraining admixture. All air-entrained fly ash concretes exhibited excellent characteristics in compressive strength (?32.0 MPa, 4641 psi at 28 days), resistance to chloride-ion penetration (moderate to low at 28 days of age) and freeze–thaw (?90 average durability factor after 300 cycles). The possible leaching of toxic elements including mercury from one fly ash sample used in this study was also evaluated using the US Environmental Protection Agency’s Toxicity Characteristic Leaching Procedure. The test results indicated that the leaching of toxic elements was much lower than the contamination level.     

Techno-economical evaluation of a rice husk ash (RHA) based sand–cement block for reducing solar conduction heat gain to a building

This paper reports on the performance of a rice husk ash (RHA) based sand–cement block. Its performance is compared with that of a standard commercial clay brick. The RHA-cement block reduces solar heat gain in buildings and the comparisons include an evaluation of room temperature, solar conduction heat transfer and economics. An appraisal of the two was conducted using two small rooms (floor area of 5.75 m²). One of the rooms was constructed using the RHA based sand–cement block wall; the other, which served as the reference, used a commercial clay brick wall. Experiments were performed throughout a period of one summer month (March) in Thailand. The results showed that the RHA based sand–cement block reduced solar heat transfer by 46 W. An economic analysis indicates that the payback period of the RHA block in tandem with a 1 ton, split-type air conditioner depends on the indoor set-point temperature. The payback period is 4.08 years when the indoor set-point temperature of 26 °C is taken.     

Durability of cementing binders based on fly ash and other wastes

The paper deals with the cementitious binders produced by blending 60–70% fly ash with fluorogypsum, hydrated lime sludge, with and without Portland cement and chemical activator in different proportions. Data show that strength development of cementitious binders takes place through formation of ettringite, C–S–H and wollastonite compounds. The durability of these binder has been studied by its performance in water and by accelerated aging i.e. alternate wetting and drying as well as by heating and cooling cycles at temperatures in the range 27–50 °C. The results indicate Lawrence of strength of binder with the increasing cyclic studies at different temperatures. The maximum fall in compressive strength was noticed at 50 °C.     

Properties of EPS RHA lightweight concrete bricks under different curing conditions

The depletion of non-renewable resources has become an alarming issue nowadays. Many environmentalists and researchers have been investigating the use of waste materials as a renewable resource for use especially as raw materials in construction. This paper reports on the potential use of waste rice husk ash (RHA) and expanded polystyrene (EPS) beads in producing lightweight concrete bricks. The RHA was used as a cementitious material since it is a lightweight reactive pozzolanic material. RHA was used as partial cement replacement, while the EPS was used as partial aggregate replacement in the mixes. Bricks of 215 mm × 102.5 mm × 65 mm in size were prepared in this study. The engineering properties of the bricks were investigated. Among the properties studied were hardened concrete density, compressive strength and water absorption of the EPS RHA concrete bricks. Scanning electron microscopy (SEM) analysis was also performed on the brick samples. Four types of curing conditions were employed in this study. These include full water curing, air dry curing, 3-day curing and 7-day curing. It was found that the properties of the bricks are mainly influenced by the content of EPS and RHA in the mix and also the curing condition used.     

Effect of shale addition on properties of sintered coal fly ash

Shale can be used as a substitute for clay in sintered fly ash, due to the similar physical and chemical property to clay. In this paper, these characteristics of sintered fly ash with or without shale (binder) were investigated by physical property, X-ray diffraction and scanning electron microscopy. The results show that shale addition ranging from 30% to 50% (in weight) can be beneficial for properties of sintered products at temperature ranging from 950 to 1050 °C. However, a higher amount of shale easily caused significant bloating at 1100 °C. Considering energy saving and best performance, the sintering mix for shale and fly ash (50% in weight respectively, the same as below) fired at 1000 °C for 2 h was an optimal option. XRD results of the sintering mix show that intensity of hercynite increases with the increasing temperature, but intensity of quartz decreases on sintering. SEM confirms that addition of shale can improve microstructure and sintering of fly ash.     

High-strength rice husk ash concrete incorporating quarry dust as a partial substitute for sand

Quarry dust is a by-product from the granite crushing process in quarrying activities. This paper presents the findings from experimental work undertaken to evaluate the suitability of quarry dust as a partial substitute for sand in high-strength concrete (HSC) containing rice husk ash (RHA). Two grades of HSC mixes, to achieve 60 MPa and 70 MPa at 28 days, were designed with and without the incorporation of RHA. Quarry dust was then used in the mixes containing RHA as a partial substitute for sand, in quantities ranging from 10% to 40%. The slump of the fresh concrete and the compressive strength development were monitored up to 28 days. Based on the results obtained, the mixes containing 20% quarry dust were chosen as the optimum mix design for both grades of concrete, which would then undergo further evaluation of their strength and mechanical properties up to one year. The results obtained in the next stage suggest that even though the use of quarry dust as a partial substitute for sand results in some minor negative effects in the compressive strength and other mechanical properties of concrete, these outcomes can easily be compensated by a good mix design and by the incorporation of RHA. The findings of the research assert that quarry dust can be used as a viable replacement material to sand to produce high-strength RHA concrete.     

Preparation and properties of an environment friendly polymer-modified waterproof mortar

A new type of environment friendly polymer-modified waterproof mortar (PMWM) was developed through adding ethylene vinyl acetate (EVA)/vinyl acetate–vinyl ester of versatic acid (Va–VeoVa) mixture (re-dispersible emulsion powder), mine tailings, quartz sand and additives to the eco-cement, which was prepared by grinding the mixture of steel slag, blast-furnace slag, fly ash and activator. The optimal material proportioning of PMWM was obtained based on the Orthogonal experiment: re-dispersible emulsion powder, 11 wt.%; cement–sand ratio, 1:3.5 (tailings/quartz sand = 1:3); EVA/Va–VeoVa ratio, 1:1; water reducing agent (based on the cement weight), 1.5 wt.%. The product conforms to JC/T 984-2005 (China professional standard: Polymer–cement waterproof mortar). Some factors influencing the characteristics of the mortar were discussed.     

Rutting evaluation of hydrated lime and SBS modified asphalt mixtures for laboratory and field compacted samples

The purpose of this study is to evaluate permanent deformation for hydrated lime and SBS modified asphalt mixtures. Control (C), 2% hydrated lime (2L), 5% SBS polymer mixtures and 2%hydrated lime–5%SBS (2L5SBS) mixtures were prepared. The Laboratoire Central des Ponts et Chaussées (LCPC) wheel tracker, also known as French Rutting Tester were realized with two different stages. Same LCPC slabs were produced. Original LCPC compactors and also field cylinder were used separately. LCPC rutting values were determined with left and right wheel loadings. Also averages were obtained with calculation. Repeated creep tests were used for these mixtures and permanent deformations were plotted for two different moisture conditioning that water immersion and freeze and thaw cycles. Diameter samples (100 mm and 150 mm) were studied in repeated creep tests. In the result that LCPC tracking values were compared with repeated creep tests in terms of sample diameters. LCPC wheel-tracking test results show that 2L5SBS mixtures reveal utmost performance according to the other mixtures types. Polymer modification increased rutting resistance of lime modified ones. Both original LCPC compactor and field cylinder compaction showed resemble results. 150 mm samples showed highest correlation (higher than R² = 0.80) between LCPC test and repeated creep test for different compaction types and different moisture conditionings.     

Influence of the use of rice husk ash on the electrical resistivity of concrete: A technical and economic feasibility study

This study investigated the behavior of apparent electrical resistivity of concrete mixes with the addition of rice husk ash using Wenner’s four electrode method. Tests included compressive strength, porosity and electrical conductivity of the pore solution. The contents of rice husk ash tested were 10%, 20% and 30% and results were compared with a reference mix with 100% Portland cement and two other binary mixes with 35% fly ash and 50% blast furnace slag. Higher contents of rice husk ash resulted in higher electrical resistivity, which exceeded those of all other samples. However, for compressive strength levels between 40 MPa and 70 MPa, the mix with 50% blast furnace slag showed the best combination of cost and performance.