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).     

Use of fine glass as ASR inhibitor in glass aggregate mortars

Demand for recycled glass has considerably decreased in recent years, particularly for mixed glass. Glass is cheaper to store than to recycle, as conditioners require expenses for the recycling process. In order to provide a sustainable solution to glass storage, a potential and incentive way would be to reuse this type of glass in concretes. Depending on the size of the glass particles used in concrete, two antagonistic behaviours can be observed: alkali–silica reaction, which involves negative effects, and pozzolanic reaction, improving the properties of concrete. The work undertaken here dealt with the use of fine particles of glass and glass aggregates in mortars, either separately or combined. Two parameters based on standardised tests were studied: pozzolanic assessment by mechanical tests on mortar samples and alkali-reactive aggregate characteristics and fines inhibitor evaluations by monitoring of dimensional changes. It is shown that there is no need to use glass in the form of fines since no swelling due to alkali–silica reaction is recorded when the diameter of the glass grains is less than 1 mm. Besides, fine glass powders having specific surface areas ranging from 180 to 540 m²/kg reduce the expansions of mortars subjected to alkali–silica reaction (especially when glass aggregates of diameters larger than 1 mm are used).     

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.     

Mechanical properties of normal and high strength concretes subjected to high temperatures and using image analysis to detect bond deteriorations

The effect of high temperatures, up to 250 °C, on mechanical properties of normal and high strength concretes with and without silica fume was investigated, and image analysis was performed on split concrete surfaces to see the change in bond strength between aggregate and mortar. Specimens were heated up to elevated temperatures (50, 100, 150, 200, 250 °C) without loading and then the residual compressive and splitting tensile strength, as well as the static modulus of elasticity of the specimens were determined. For normal strength concrete residual mechanical properties started to decrease at 100 °C, while using silica fume reduced the losses at high temperatures. In terms of percent residual properties, high strength concrete specimens performed better than normal strength concrete specimens for all heating cycles. Image analysis studies on the split surfaces have been utilized to investigate the effect of high temperatures on the bond strength between aggregate and mortar. Image analysis results showed that reduced water–cement ratio and the use of silica fume improved the bond strength at room temperature, and created more stable bonding at elevated temperatures up to 250 °C.     

Use of power plant bottom ash as fine and coarse aggregates in high-strength concrete

In this study, experiments have been carried out to evaluate the utilization of bottom ash (by-product of power plant) as fine and coarse aggregates in high-strength concrete with compressive strength of 60–80 MPa. Firstly, the chemical and physical characteristics of bottom ash particles, such as chemical compositions, specific gravity and SEM images, were investigated. Further experiments were conducted by replacing fine and coarse bottom ash with normal sand and gravel varying in percentages (25%, 50%, 75%, and 100%). The effect of fine and coarse bottom ash on the flow characteristics and density of concrete mixture was investigated in the aspect of particle shapes and paste absorption of bottom ash. Mechanical properties, such as compressive strengths and modulus of elasticity and flexural strength of high-strength concrete with bottom ash were evaluated. It was found that the slump flow of fresh concrete was slightly decreased from 530 mm to 420 mm when coarse bottom ash was replaced 100% of normal coarse aggregates, while fine bottom ash did not affect the slump flow. Moreover, it also showed that both of fine and coarse bottom ash aggregates had more influence on the flexural strength than compressive strength.     

Study of high performance autoclaved shell-aggregate from propylene oxide sludge

This study focuses on the comprehensive utilization of propylene oxide sludge (POS). High performance propylene oxide sludge aggregate (POSA), whose main hydrated phase is tobermorite, was prepared by the hydrothermal synthesis of POS and silica materials under the condition of 180 °C saturated steam. The factors affecting the performance of the aggregate were investigated systematically by orthogonal experiments, thus aggregate with cylinder compressive strength between 6.14 and 13.52 MPa, bulk density between 882 and 1163 kg/m³, apparent density between 1515 and 1916 kg/m³, 1 h water absorption rate between 4% and 14%, 24 h water absorption rate between 11% and 19%, the mass loss of freezing and thawing between 1.63% and 3.92% was achieved. By single-factor analysis, it was shown that cylinder compressive strength and specific strength of propylene oxide sludge shell-aggregate (POSS-A) increases by 21.3% and 13.9%, respectively, in contrast to the POSA with no shell. At the same time, 1 h water absorption rate and 24 h water absorption rate decreases by 57% and 20%, respectively. The compressive strength of the concrete with POSS-A as coarse aggregate reaches 80 MPa, which is 8.1% higher than that of the crushed stone concrete. In addition, the density gets lowered by 17%. The HVEP results of analysis of the aggregate imply that heavy metals are solidified inside aggregate and the POSA thus fabricated is non-hazardous for construction use.     

The role of industrial by-products in self-compacting concrete

The development of self-compacting concrete is considered as a milestone achievement in concrete technology due to several advantages. In order to be self-compactable the fresh concrete must show high fluidity besides good cohesiveness. For the purpose of evaluating these properties, several concrete mixtures were prepared with a water to cement ratio of 0.45 in the presence of an acrylic-based superplasticizer at a dosage ranging from 1% to 2% by weight of very fine material fraction (maximum 150 μm). Either limestone powder or fly ash or recycled aggregate powder (that is a powder obtained from the rubble recycling process) were used as mineral addition, in order to assure adequate rheological properties, in terms of cohesiveness, in the self-compacting concretes. Preliminary rheological tests were carried out on cement pastes containing these mineral additions. In some cases, recycled instead of natural aggregate was used by substituting either the coarse or the fine aggregate fraction. The fresh concrete properties were evaluated through slump flow, L-box test and segregation resistance. Compressive strength of concrete was determined at 1, 3, 7 and 28 days of wet curing. Results obtained showed that an optimization of self-compacting concrete mixture seems to be achievable by the simultaneous use of rubble powder and coarse recycled aggregate with improved fresh concrete performance and unchanged concrete mechanical strength.     

Fire extinguishing properties of novel ferrocene/surfynol 465 dispersions

This paper reports a novel fire-extinguishing agent: an aqueous dispersion of fine ferrocene particles. In this study, the ferrocene–water–surfactant dispersions were prepared to optimize the gas-phase concentration of ferrocene, and their ability to extinguish heptane fires was examined. The fire-extinguishing efficiency was characterized by three parameters: the ferrocene concentration in the dispersion (0–175 ppm), the surfactant used, and the ferrocene particle size (d₅₀=10.4, 11.4, 21.5, and 68.8 μm). The results indicated that (1) the ferrocene (d₅₀=10.4 mm)–water–surfynol 465 dispersion is the most stable among the dispersions tested, (2) the ferrocene–water–surfynol 465 dispersions have an optimal value of ferrocene concentration regarding the extinguishing time, and (3) in the ferrocene particle size range of 10.4–21.5 μm, the minimum extinguishing time of the ferrocene–water–surfynol 465 dispersions is remarkably shorter (1.2 s) than those observed when using a conventional wet chemical agent (45 wt% aqueous solution of potassium carbonate, 12.9 s).     

Determination of smoldering time and thermal characteristics of firebrands under laboratory conditions

The laboratory experiment was conducted to simulate the transfer of smouldering particles produced in forest wildfires by a heated gas flow. The pine bark pieces with the linear dimensions L=(15; 20; 30) mm and a thickness of h=(4−5) mm were selected as model particles. The rate and temperature of the incident flow varied in the range of 1–3 m/s and 80–85 °C, respectively. The temperature of the samples was recorded using a thermal imager. To determine the minimum smouldering temperature of pine bark, the thermal analysis was conducted. The minimum smouldering temperature of pine bark was found to be 190 °C. This temperature will cause thermal decomposition of bark only at the first stage (oxidation of resinous components). In the study the smouldering time, the temperature and the weight of samples were obtained and analyzed under various experimental conditions. The data analysis shows that the increase in the particle size leads to the decrease in their mass loss, and the rate change of the incident flow does not practically influence the mass change. For particles with the linear dimensions of 10 mm and 20 mm, the mass varies from 6% to 25%. The maximum mass loss is observed for the flows with a rate of 1 and 2 m/s. The results have shown that the increase in the particle size leads to the increase in the smouldering time. The position of the particle plays an important role, the effect of which increases with increasing the particle size. The calculations showed that the smouldering time of bark samples is long enough for the particles to serve as new sources of spot fires. The particles were found to be transported to a distance of 218 m from the fire line which can certainly influence the propagation of the fire front.     

Influence of mineral additions on the performance of 100% recycled aggregate concrete

A judicious use of resources, by using by-products and waste materials, and a lower environmental impact, by reducing carbon dioxide emission and virgin aggregate extraction, allow to approach sustainable building development. Recycled aggregate concrete (RAC) containing supplementary cementitious materials (SCM), if satisfactory concrete properties are achieved, can be an example of such sustainable construction materials.In this work concrete specimens were manufactured by completely replacing fine and coarse aggregates with recycled aggregates from a rubble recycling plant. Also RAC with fly ash (RA + FA) or silica fume (RA + SF) were studied.Concrete properties were evaluated by means of compressive strength and modulus of elasticity in the first experimental part. In the second experimental part, compressive and tensile splitting strength, dynamic modulus of elasticity, drying shrinkage, reinforcing bond strength, carbonation, chloride penetration were studied. Satisfactory concrete properties can be developed with recycled fine and coarse aggregates with proper selection and proportioning of the concrete materials.     

Mortars with nano-SiO2 and micro-SiO2 investigated by experimental design

This paper reports the effects of nanosilica (nS) and silica fume (SF) on rheology, spread on flow table, compressive strength, water absorption, apparent porosity, unrestrained shrinkage and weight loss of mortars up to 28 days. Samples with nS (0–7 wt.%), SF (0–20 wt.%) and water/binder ratio (0.35–0.59), were investigated through factorial design experiments. Nanosilica with 7 wt.% showed a faster formation of structures during the rheological measurements. The structure formation influences more yield stress than plastic viscosity and the yield stress relates well with the spread on table. Compressive strength, water absorption and apparent porosity showed a lack of fit of second order of the model for the range interval studied. In addition, the variation of the unrestrained shrinkage and weight loss of mortars do not follow a linear regression model. The maximum unrestrained shrinkage increased 80% for nS mortars (7 days) and 54% (28 days) when compared to SF mortars in the same periods.     

Effects of crushed glass cullet sizes,casting methods and pozzolanic materials on ASR of concrete blocks

The aim of this study is to investigate the influence of using different particle sizes of recycled glass, casting methods and pozzolanic materials in reducing the expansion due to alkali-silica reaction (ASR) of concrete blocks prepared with the use of crushed glass as fine aggregate. In this work, 25 × 25 × 285 mm mortar bar specimens were prepared using conventional wet-mixed and dry-mixed methods. Except for the control mortar bar, all the specimens were prepared by completely replacing river sand with different particle sizes of recycled glass. In addition, the influence of fly ash (PFA) and metakaolin (MK) content on the reduction of ASR expansion was also investigated. The flexural strength of the mortar bar specimens before and after they had been exposed to 1N NaOH solution was determined to complement the results of ASR expansion test. SEM was performed to examine the microstructure as well as nature of the cement binder-glass interfacial zone. The results reveal that ASR expansion reduced with reducing particle size of glass used. For the same given mix proportion, the dry-mixed method resulted in 44% less expansion when compared with the wet-mixed method. Both PFA and MK were demonstrated to be able to significantly reduce ASR expansion of the concrete glass blocks.     

Mechanical and microstructural characterization of an alkali-activated slag/limestone fine aggregate concrete

Four limestone-based, alkali-activated slag fine aggregate concretes, two of which contained amorphous silica in the form of diatomaceous earth, were fabricated using different activating solutions (NaOH/waterglass or Na₂CO₃). Emphasis in this work was placed on using simple manufacturing methods and widely available materials, to ensure that these formulae are practical as construction materials in the developing world. Although cured only at room temperature, these fine aggregate concretes have good compressive strengths (～45 MPa) and their tensile strengths increased from ～2.6 MPa after 1 day of curing to ～4 MPa after 28 day for the NaOH-activated formulae. Samples activated with Na₂CO₃ had negligible tensile strengths after 1 day, increasing to ～2.5 MPa after 28 day. The main cementing phase was shown to be calcium–silicate–hydrates in all formulae; those activated with Na₂CO₃ also showed the presence of hydrotalcite. No evidence of geopolymeric phases was found, though incorporation of Na to form N–S–H that balance charges arising from Al substitution of Si in C–S–H is likely. Despite the short (～120 s) pot life of the strongest formula, NaCl was shown to be an effective retarding agent, which reduced the strengths of different formulae, at worst, by less than 25% after 28 day of curing.     

Effect of concrete mixing parameters on propagation of ultrasonic waves

An experimental study was conducted to evaluate the effect of concrete aggregate gradation, water–cement ratio, and curing time on measured ultrasonic wave velocity (UPV). 30 × 30 × 10 cm Portland cement concrete slabs were cast for ultrasonic evaluation, while 10 cm diameter by 20 cm height cylinders were cast for compressive strength evaluation The slabs and cylinders were prepared using Portland cement and limestone aggregate. Two slabs were cast from each combination of coarse aggregate gradations and water cement ratio (0.40, 0.45, 0.50, and 0.55). Four ASTM gradations were considered, ASTM No: 8, 67, 56, and 4. These gradations have nominal maximum aggregate size 25, 4.75, 19.3, and 12.5 mm, respectively.The ultrasonic equipment used in this study was the portable ultrasonic non-destructive digital indicating tester (PUNDIT) with a generator having an amplitude of 500 V producing 54 kHz waves. The time needed to transfer the signal between the transducers was recorded and used to calculate the signal velocity, which was used as a parameter in the evaluation. Ultrasonic measurements were performed at 3, 7, 28, and 90 days after concrete casting.The results of the analysis indicated that water–cement ratio was found to have a significant effect on UPV. The UPV was found to decrease with the increase of water cement ratio. Aggregate gradation was also found to have significant effect on UPV. In general, the larger the aggregate size used in preparing Portland cement concrete, the higher the measured velocity of ultrasonic waves. Also, UPV was found to be increased as concrete curing time increased. Concrete compressive strength was found to be significantly affected by water–cement ratio and coarse aggregate gradation. Lower water–cement ratio produced higher concrete strength. Also, the concrete compressive strength increased as maximum aggregate size decreased.     

Water absorption,permeability, and resistance to chloride-ion penetration of lightweight aggregate concrete

This paper presents an experimental study to evaluate effect of cumulative lightweight aggregate (LWA) content (including lightweight sand) in concrete [water/cement ratio (w/c) = 0.38] on its water absorption, water permeability, and resistance to chloride-ion penetration. Rapid chloride penetrability test (ASTM C 1202), rapid migration test (NT Build 492), and salt ponding test (AASHTO T 259) were conducted to evaluate the concrete resistance to chloride-ion penetration. The results were compared with those of a cement paste and a control normal weight aggregate concrete (NWAC) with the same w/c and a NWAC (w/c = 0.54) with 28-day compressive strength similar to some of the lightweight aggregate concrete (LWAC). Results indicate that although the total charge passed, migration coefficient, and diffusion coefficient of the LWAC were not significantly different from those of NWAC with the same w/c of 0.38, resistance of the LWAC to chloride penetration decreased with increase in the cumulative LWA content in the concretes. The water penetration depth under pressure and water sorptivity showed, in general, similar trends. The LWAC with only coarse LWA had similar water sorptivity, water permeability coefficient, and resistance to chloride-ion penetration compared to NWAC with similar w/c. The LWAC had lower water sorptivity, water permeability and higher resistance to chloride-ion penetration than the NWAC with similar 28-day strength but higher w/c. Both the NWAC and LWAC had lower sorptivity and higher resistance to chloride-ion penetration than the cement paste with similar w/c.     

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.     

Effect of red mud addition on the rheological behaviour and on hardened state characteristics of cement mortars

This paper reports on the use of red mud (RM) in mortars, applying design of experiments. Portland cement was replaced up to 50 wt.% RM, adjusting the relative amount of water (34–38 wt.%) in order to get mortars with suitable workability as defined by rheometry and flow table measurements. Temperature of hydration, compressive strength and water absorption were also determined. RM decreases the workability and increases the torque, but causes lower impact than water variation. The effect on initial yield stress depends on water content. Mortars with similar spread on table show different behaviour along the rheology test. Values of spread on table follow a quadratic model and RM exhibited an interactive effect with water. RM did not change the hydration process, but above 20% the maximum temperature decreases. The reduction of compressive strength is not constant and depends on the water added. Its variation also follows a quadratic model.     

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.     

Durability design and performance of self-consolidating lightweight concrete

In terms of the durability, the reduction in cement paste is crucial to both volume stability and long-term performance of concrete. The objective of this paper is to compare the performance of lightweight concrete under different w/cm ratio and different cement paste content. The slump and slump flow spread of fresh self-consolidating lightweight concrete (SCLWC) are designed to be within 230–270 and 550–650 mm, respectively. The test results indicate that the 91-day compressive strength of SCLWC is up to 56 MPa when cement content is 386 kg/m³ and water content is 150 kg/m³. If enough cement paste is used, then the less the paste amount and the denser the packing of aggregate, the higher the strength efficiency of cement and the electric resistance, and the lower the chloride ion penetrability capacity of SCLWC.     

Characteristics of mortar and concrete containing fine aggregate manufactured from recycled waste polyethylene terephthalate bottles

This paper presents the development of lightweight aggregate concrete using fine aggregate that is manufactured from recycled waste polyethylene terephthalate (PET) bottles. Investigations on waste PET lightweight aggregate concrete included three phases: examination of the properties of waste PET lightweight aggregates (WPLA), analysis of the properties of mortar when WPLA was used as fine aggregate, and analysis of the properties of concrete when WPLA was used as fine aggregate. The results of the first phase showed that the WPLA had a density of 1390 kg/m³, a water absorption of 0% and a bulk density of 844 kg/m³. WPLA fineness modulus (F.M.), however, was 4.11, which is higher than the F.M. of river sand. This is because the WPLA was single graded. The results of the second phase showed that for the mortar, in which the WPLA was used as a fine aggregate, the flow value increased, while the compressive strength decreased proportionally to the addition of WPLA with elapsed time. In addition, the amount of water absorption by unit area was higher than for the control mortar (without WPLA) when the WPLA content was either 40% or 60%. For the third phase, the results showed that the slump of the WPLA concrete increased as the WPLA content increased regardless of the water-cement ratio (W/C). In comparison to the control concrete, the 28-day WPLA concrete compressive strength decreased by 5%, 15% and 30%, with an increase of WPLA content of 25%, 50% and 75%, respectively. In addition, for a W/C of 0.49, the structural efficiency (compressive strength/density ratio) of the concrete containing 25% of WPLA was higher than that for the control concrete.