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.     

CDW recycled aggregate renderings: Part II – Analysis of the effect of materials finer than 75 μm under accelerated aging performance

Quality control of the performance of renderings made up of construction and demolition waste (CDW) recycled aggregates needs to be improved as CDW recycling can prove to be an alternative to waste disposal in developing countries. This experimental work focuses the effectiveness of a mix design method to control and analyze the recycled aggregate composition influence on the performance of mortars and renderings. Leveling time in the placement of renderings was also studied. The mix design method of mortars takes into account two parameters: the “aggregates and plasticizing materials to cement ratio” and “the total materials finer than 75 μm” in the dry mortar. In Part I of this study [Construction and Building Materials, submitted to publishing] the basic properties of mortars of several mixes were analyzed for a constant cement content around 155 ± 10 kg/m³. The performance of renderings is the scope of Part II of this paper. The initial bond strength and visible drying cracks under laboratory conditions were first analyzed for renderings applied on masonry panels with two times of leveling during placement. After five months, accelerated aging of renderings was carried out. Ten wetting–drying cycles upon thermal shock, from 80 °C to laboratory room temperature, were applied to the masonry panels, and cracks were assessed for each cycle. Bond tensile strength was not affected by the thermal shock, but additional cracks were seen on the renderings. The mix design parameters of the mortars and their hardened state properties were related to the cracking of the renderings. The results show that the parameters “total materials finer than 75 μm” and “aggregate to cement ratio” can be used for the mix design of mortars with recycled CDW aggregates. The increase in tensile strength and the reduction in the content of total fines smaller than 75 μm have proved efficient parameters to control cracking of renderings under thermal shock. Leveling time during rendering placement was a secondary parameter for cracking behavior.     

Effects of size fraction on composition and fundamental properties of Portland cement

To characterize roles of size fraction of Portland cement to its properties, Portland cement was classified into several fractions by air classifier. Then composition and hydration related properties of each Portland cement fraction were investigated. The results show deviation of chemical and mineral compositions occurs during classification. Both fine and coarse Portland cement fractions have undesirable strength contribution. Portland cement fractions falling in the range of 8–24 μm have low water requirement, high hydration rate and highest 28 days compressive strength. Thus Portland cement is recommended to be arranged in middle fraction (8–24 μm), while high activity supplementary cementitious materials (SCMs) and low activity SCMs (or inert fillers) are suggested to be arranged in fine and coarse fractions, respectively, by which Portland cement can be replaced by SCMs (or inert fillers) in larger extent without or with little performance loss.     

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.     

Influence of pozzolan from various by-product materials on mechanical properties of high-strength concrete

This paper presents experimentally investigated the effects of pozzolan made from various by-product materials on mechanical properties of high-strength concrete. Ground pulverized coal combustion fly ash (FA), ground fluidized bed combustion fly ash (FB), ground rice husk–bark ash (RHBA), and ground palm oil fuel ash (POFA) having median particle sizes less than 11 μm were used to partially replace Portland cement type I to cast high-strength concrete. The results suggest that concretes containing FA, FB, RHBA, and POFA can be used as pozzolanic materials in making high-strength concrete with 28-day compressive strengths higher than 80 MPa. After 7 days of curing, the concretes containing 10–40% FA or FB and 10–30% RHBA or POFA exhibited higher compressive strengths than that of the control concrete (CT). The use of FA, FB, RHBA, and POFA to partially replace Portland cement type I has no significant effect on the splitting tensile strength and modulus of elasticity as compared to control concrete or silica fume concretes. This results suggest that the by-products from industries can be used to substitute Portland cement to produce high-strength concrete without alteration the mechanical properties of concrete.     

Assessment of the effects of rice husk ash particle size on strength,water permeability and workability of binary blended concrete

This study develops the compressive strength, water permeability and workability of concrete by partial replacement of cement with agro-waste rice husk ash. Two types of rice husk ash with average particle size of 5 micron (ultra fine particles) and 95 micron and with four different contents of 5%, 10%, 15% and 20% by weight were used. Replacement of cement up to maximum of 15% and 20% respectively by 95 and 5 μm rice husk ash, produces concrete with improved strength. However, the ultimate strength of concrete was gained at 10% of cement replacement by ultra fine rice husk ash particles. Also the percentage, velocity and coefficient of water absorption significantly decreased with 10% cement replacement by ultra fine rice husk ash. Moreover, the workability of fresh concrete was remarkably improved by increasing the content of rice husk ash especially in the case of coarser size. It is concluded that partial replacement of cement with rice husk ash improves the compressive strength and workability of concrete and decreases its water permeability. In addition, decreasing rice husk ash average particle size provides a positive effect on the compressive strength and water permeability of hardened concrete but indicates adverse effect on the workability of fresh concrete.     

Effect of micro-silica loading on the mechanical and acoustic properties of cement pastes

This study aimed at investigating the role of ultra fine sand (UFS) in enhancing the mechanical and acoustic properties of cementitious pastes. The microstructural origin of these properties was also identified and compared to the conventional materials. The maximum particle size of the UFS used was 100 μm (100% passing) while 50% of the UFS had less than 20 μm in diameter. Ordinary Portland cement (OPC) was partially substituted by UFS at 1%, 2%, 3%, 4%, 5%, 7.5% and 10% by weight of binder. The blended compounds were prepared using the standard water of consistency. Test samples with dimension of 20 × 20 × 20 mm and 40 × 40 × 160 mm were cast for compression and bending strengths tests, respectively. Circular samples with diameters of about 100 and 29 mm and average thickness of about 30 mm were used for sound absorption tests. All samples were kept in molds for 24 h, and then de-molded and allowed to cure in water for 28 days. The specimens were dried at a temperature of 105 °C for 24 h in an oven before testing. It was found that as the loading of UFS increases both the compressive and bending strength increase up to about 5% UFS loading, then a decrease in these properties was observed. This can be attributed to the pozzolanic effect of UFS resulting in enhancing the chemical reaction between free lime in cement and silica producing more hydration products that makes the paste more homogeneous and dense. In addition, the dispersed UFS has improved the filling effect allowing denser packing of the paste. These dense microstructural features were captured by scanning electron microscope (SEM) examination of the 5% UFS modified compound. The results also showed that, the sound absorption and noise reduction coefficient (NRC) for modified cement paste decreases with the increase of UFS up to 5% and this may be due to the decrease in porosity. However, the NRC began to increase at UFS loadings of 7.5% and 10% due to the increase in the porosity of the compounds.     

Lime based steam autoclaved fly ash bricks

About 10 million tonnes of fly ash are produced yearly as waste from coal fired thermal power plants in Turkey. Only a small portion of this waste is utilized as a raw material in the production of cement and concrete. In this study, Seyitömer power plant fly ash was investigated in the production of light weight bricks. Fly ash, sand and hydrated lime mixtures were steam autoclaved under different test conditions to produce brick samples. An optimum raw material composition was found to be a mixture of 68% fly ash, 20% sand and 12% hydrated lime. The optimum brick forming pressure was 20 MPa. The optimum autoclaving time and autoclaving pressure were found 6 h and 1.5 MPa, respectively. The compressive strength, unit volume weight, water absorption and thermal conductivity of the fly ash–sand–lime bricks obtained under optimum test conditions are 10.25 MPa, 1.14 g/cm³, 40.5% and 0.34 W  m⁻¹ K⁻¹ respectively. The results of this study suggested that it was possible to produce good quality light weight bricks from the fly ash of Seyitömer power plant.     

The study of using rice husk ash to produce ultra high performance concrete

The limited available resource and the high cost of silica fume (SF) in producing ultra high performance concrete (UHPC) give the motivation for searching for the substitution by other materials with similar functions, especially in developing countries. Rice husk ash (RHA), an agricultural waste, is classified as “a highly active pozzolan” because it possesses a very high amount of amorphous SiO₂ and a large surface area. The possibility of using RHA to produce UHPC was investigated in this study. The result shows that the compressive strength of UHPC incorporating RHA, with the mean size between 3.6 μm and 9 μm, can be achieved in excess of 150 MPa with normal curing regime. The interesting point is that the effect of RHA on the development of compressive strength of UHPC is larger than that of SF. Besides, the sample incorporating the ternary blend of cement with 10% RHA and 10% SF showed better compressive strength than that of the control sample without RHA or SF. This blend proved to be the optimum combination for achieving maximum synergic effect.     

The relationship between autogenous shrinkage and pore structure of cement paste with mineral admixtures

In this paper, the combination of fly ash and silica fume, or fly ash and blast furnace slag were used as the composite mineral admixtures in cement paste. The autogenous shrinkage and the pore structure of the hardened cement paste with mineral admixtures were tested, and the relationship of the autogenous shrinkage and pore structure also was discussed. The results indicate that fly ash can reduce the autogenous shrinkage, and silica fume can increase the autogenous shrinkage, and the effect of blast furnace slag is between the two above; although both silica fume and blast furnace slag can weaken the porosity and the mean diameter of cement paste, and increase the volumetric percentage of pores whose diameter is between 5 and 50 nm and pore specific surface, silica fume is better than blast furnace slag in changing the pore structure. The relationship between the autogenous shrinkage and volumetric percentage of pores whose diameter is between 5 and 50 nm is obviously proportional.     

Lightweight concretes of activated metakaolin-fly ash binders,with blast furnace slag aggregates

This work investigated geopolymeric lightweight concretes based on binders composed of metakaolin with 0% and 25% fly ash, activated with 15.2% of Na₂O using sodium silicate of modulus SiO₂/Na₂O = 1.2. Concretes of densities of 1200, 900 and 600 kg/m³ were obtained by aeration by adding aluminium powder, in some formulations lightweight aggregate of blast furnace slag was added at a ratio binder:aggregate 1:1; curing was carried out at 20 and 75 °C. The compressive and flexural strength development was monitored for up to 180 days. The strength diminished with the reduction of the density and high temperature curing accelerated strength development. The use of the slag had a positive effect on strength for 1200 kg/m³ concretes; reducing the amount of binder used. The thermal conductivity diminished from 1.65 to 0.47 W/mK for densities from 1800 to 600 kg/m³. The microstructures revealed dense cementitious matrices conformed of reaction products and unreacted metakaolin and fly ash. Energy dispersive spectroscopy and X-ray diffraction showed the formation of amorphous silicoaluminate reaction products.     

Analysis of strength development in cement-stabilized silty clay from microstructural considerations

This paper analyzes the strength development in cement-stabilized silty clay based on microstructural considerations. A qualitative and quantitative study on the microstructure is carried out using a scanning electron microscope, mercury intrusion pore size distribution measurements, and thermal gravity analysis. Three influential factors in this investigation are water content, curing time, and cement content. Cement stabilization improves the soil structure by increasing inter-cluster cementation bonding and reducing the pore space. As the cement content increases for a given water content, three zones of improvement are observed: active, inert and deterioration zones. The active zone is the most effective for stabilization where the cementitious products increase with cement content and fill the pore space. In the active zone, the effective mixing state is achieved when the water content is 1.2 times the optimum water content. In this state, the strength is the greatest because of the highest quantity of cementitious products. In the short stabilization period, the volume of large pores (larger than 0.1 μm) increases because of the input of coarser particles (unhydrated cement particles) while the volume of small pores (smaller than 0.1 μm) decreases because of the solidification of the cement gel (hydrated cement). With time, the large pores are filled with the cementitious products; thus, the small pore volume increases, and the total pore volume decreases. This causes the strength development over time.     

Applications of sewage sludge ash and nano-SiO2 to manufacture tile as construction material

In this study, various portions of potter’s clay and porcelain clay were replaced with incinerated sewage sludge ash (ISSA) to manufacture sludge ash tile specimens. We used these tiles to investigate the effect of introducing nano-SiO₂ particles as strengthening additives in the clay–ISSA materials. Percentages of ISSA in the porcelain or potter’s clay-based materials ranged from 0% to 50%, and fractions of nano-SiO₂ additives range from 0% to 3%. Tile specimens were manufactured from the different clay–ISSA–additive mixtures and sintered at kiln temperatures of 1000 °C and 1100 °C. Mechanical tests were performed to measure shrinkage, water absorption, abrasion, and bending strength. The sample microstructure was investigated using scanning electron microscopy (SEM). Chemical compositions of the tile specimens were characterized with X-ray diffraction. Results indicate that water absorption of porcelain and potter’s clay-based tiles was reduced when samples were fired at the higher kiln temperature, dropping to less than 12% in porcelain tiles at a kiln temperature of 1100 °C. Kiln temperature appeared to have less influence on the tiles made from potter’s clay. With the addition of nano-SiO₂ additive, the bending strengths of both types of tiles were increased, with the strengthening effect more pronounced in potter’s clay tiles when compared to porcelain clay tiles.     

Effect of magnesium oxychloride cement on stabilization/solidification of sewage sludge

Solidification/stabilization (S/S) is considered to be a well-established disposal technique to reduce sludge handling and disposal obstacles. In this work, the sewage sludge was solidified at variable proportions with magnesium oxychloride cement (denoted as MOC thereinafter) as reagent. The mortar prism samples of 40 × 40 × 160 mm in dimension were prepared and hardened for 24 h at room temperature. Unconfined compressive strength after 10-day curing time, initial and final setting time, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and toxicity leachability of the samples, were used to characterize the macroscopic and microscopic effects caused by the solidified products on the MOC hydration process. The results revealed that the magnesium hydration of phase 3, phase 5 and other hydration components in CS developed a crystallizing network in the hydrated solidified products, which not only enhanced the strength of CS but also prevented the precipitation of heavy metal ions from CS.     

Effects of CaO addition on lightweight aggregates produced from water reservoir sediment

Lightweight aggregates were produced from water reservoir sediment with various amounts of CaO at calcining temperatures of 1170 °C–1230 °C. It was found that C–S–H gel did not form with CaO addition. The bulk density and compressive strength of the lightweight aggregates meet the regulations for lightweight structural concrete. The properties of samples with 1% CaO by weight calcined at 1200 °C match those of a commercial product. Water adsorption and compressive strength decreased with increasing CaO addition since more of the glassy phase formed, which sealed pores and led to few connections between pores.     

Interfacial interactions in concretes with silica fume and SBR latex

This paper deals with the effect of silica fume and styrene-butadiene latex (SBR) on the microstructure of the interfacial transition zone (ITZ) between Portland cement paste and aggregates (basalt). Scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis system (EDX) was used to determine the ITZ thickness. In the plain concrete a marked ITZ around the aggregate particles (55 μm) was observed, while in concretes with silica fume or latex SBR the ITZ was less pronounced (35–40 μm). However, better results were observed in concretes with silica fume and latex SBR (20–25 μm).     

Characterization of marble powder for its use in mortar and concrete

A powder obtained as a by-product of marble sawing and shaping was characterized from a chemical and physical point of view in order to use it as mineral addition for mortars and concretes, especially for self-compacting concrete. This marble powder showed a very high Blaine fineness value of about 1500 m²/kg, with 90% of particles finer than 50 μm and 50% under 7 μm. For rheological studies, several cement pastes were prepared using marble powder, with and without the addition of an acrylic-based superplasticizer. Water to cementitious materials ratio was also varied. In order to evaluate the effects of the marble powder on mechanical behaviour, many different mortar mixtures were tested, all prepared with sand to cement ratio of 3:1 at about the same workability. Mixtures were evaluated based upon cement or sand substitution by the marble powder. Results obtained show that 10% substitution of sand by the marble powder provided maximum compressive strength at about the same workability.     

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.     

Influence of class F fly ash on the abrasion–erosion resistance of high-strength concrete

This study investigates the abrasion–erosion resistance of high-strength concrete (HSC) mixtures in which cement was partially replaced by four kinds of replacements (15%, 20%, 25% and 30%) of class F fly ash. The mixtures containing ordinary Portland cement were designed to have 28 days compressive strength of approximately 40–80 MPa. Specimens were subjected to abrasion–erosion testing in accordance with ASTM C1138. Experimental results show that the abrasion–erosion resistances of fly ash concrete mixtures were improved by increasing compressive strength and decreasing the ratio of water-to-cementitious materials. The abrasion–erosion resistance of concrete with cement replacement up to 15% was comparable to that of control concrete without fly ash. Beyond 15% cement replacement, fly ash concrete showed lower resistance to abrasion–erosion compared to non-fly ash concrete. Equations were established based on effective compressive strengths and effective water-to-cementitious materials ratios, which were modified by cement replacement and developed to predict the 28- and 91-day abrasion–erosion resistance of concretes with compressive strengths ranging from approximately 30–100 MPa. The calculation results are compared favorably with the experimental results.     

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.