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.     

Effects of calcination temperature of kaolinite clays on the properties of geopolymer cements

The aim of this work is to determine the most convenient calcination temperature of kaolinite clays in view of producing geopolymer cements. In this light, the clay fractions of three kaolin minerals were used. The clay fractions were characterized (chemical and thermal analyses and X-ray diffraction) and then calcined in the temperature range of 450 and 800 °C. The obtained amorphous materials were dissolved in a strongly alkaline solution in order to produce geopolymer cements whose pastes were characterized by determining their setting time, linear shrinkage and compressive strength. Hardened geopolymer cement paste samples were also submitted to X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses. The setting time of geopolymer cement pastes produced from the clay fractions calcined at 450 °C was very long (test samples could be handled easily only after 21 days at the ambient atmosphere of the laboratory). For the clay fractions calcined between 500 and 700 °C, the setting time of geopolymer cement pastes reduced with increasing temperature and varied between 130 and 40 min. Above 700 °C, the setting time began to increase. The linear shrinkage of the hardened geopolymer cement paste samples aged between 21 and 28 days attained its lowest value around 700 °C. Above 700 °C, the linear shrinkage began to increase. The compressive strength of the hardened geopolymer cement paste samples was between 11.9 and 36.4 MPa: it increased with samples from the clay fractions calcined between 500 and 700 °C but dropped above 700 °C.It can be concluded that the most convenient temperature for the calcination of kaolinite clays in view of producing geopolymer cements is around 700 °C.     

Determination of the optimum conditions for tire rubber in asphalt concrete

The Taguchi method was used to determine optimum conditions for tire rubber in asphalt concrete with Marshall Test. The tire rubber in asphalt concrete was explored under different experimental parameters including tire rubber gradation (sieve #10–40), mixing temperature (155–175 °C), aggregate gradation (grad. 1–3), tire rubber ratio (0–10% by weight of asphalt), binder ratio (4–7% by weight of asphalt), compaction temperature (110–135 °C), and mixing time (5–30 min). The optimum conditions were obtained for tire rubber gradation (sieve #40), mixing temperature (155 °C), aggregate gradation (grad. 1), tire rubber ratio (10%), binder ratio (5.5%), compaction temperature (135 °C), mixing time (15 min).     

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.     

Production of non-constructive concrete blocks using contaminated soil

In this research, a heavily contaminated humus-rich peat soil and a lightly contaminated humus-poor sand soil, extracted from a field location in the Netherlands, are immobilized. These two types of soil are very common in the Netherlands. The purpose is to develop financial feasible, good quality immobilisates, which can be produced on large scale.To this end, two binder combinations were examined, namely slag cement with quicklime and slag cement with hemi-hydrate. The mixes with hemi-hydrate proved to be better for the immobilization of humus rich soils, having a good early strength development. The heavily contaminated soil with 19% humus (of dm) could not be immobilized using 398 kg slag cement and 33 kg quicklime per m³ concrete mix (binder = 38.4% dm soil). It is possible to immobilize this soil using 480 kg binder (432 kg slag cement, 48 kg quicklime) per m³ of mix (58.2% dm). An alternative to the addition of extra binder (slag cement with quicklime) is mixing the soil with sand containing particles in the range of 0–2 mm. This not only improved the compressive strength of the immobilisates, but also reduced the capillary absorption. All the mixes with the lightly contaminated soil were cost-effective and suitable for production of immobilisates on a large scale. These mixes had good workability, a good compressive strength and a low capillary absorption. The leaching of all mixes was found to be much lower than allowed by the regulations. Given these results, the final mixes in the main experiment fulfilled all the financial and technical objectives.     

Characterization of concrete blocks containing petroleum-contaminated soils

This paper presents the results of a study on the potential use of petroleum-contaminated soil (PCS) in the manufacturing of concrete blocks. PCS was obtained from Fahud asset area in northern Oman, where contaminated soils are typically transported for treatment. Hollow blocks of size 400 × 200 ×200 mm, widely used in Oman, were manufactured with a mix proportion of 1:2:4:0.8 for cement, coarse aggregate, sand, and water, respectively. The coarse aggregate had a 10 mm maximum aggregate size. PCS was subjected to the toxicity characteristic leaching procedure (TCLP). The chemical analysis of the extract indicated that the concentrations of metals and organic compounds did not exceed the maximum contaminant levels set by USEPA for TCLP extracts. Different mixes were prepared by replacing the sand with PCS with percentages up to 80% by sand weight in the mix. Five different tests were conducted on the concrete blocks: density, compressive strength, absorption, compressive strength of a masonry column, and thermal conductivity. The compressive strength test was conducted after 14 and 28 days of curing. The other tests were performed after 28 days of curing. Results indicated that PCS can be used with a replacement percentage up to 60% to produce concrete blocks meeting the Omani Standard specifications. The results also indicate potential deterioration when more than 60% PCS are used.     

Properties of sintered low calcium bottom ash aggregate with clay binders

This paper focuses on the properties of sintered aggregates with low calcium bottom ash from coal fired thermal power plants using a wide range of clay binders through pelletization process. The experimental runs were designed using central composite design of response surface methodology. The aggregate was produced using a disc pelletizer. The pelletized aggregate was sintered at 800–1100 °C for 30–120 min. Sintered aggregates were tested for bulk density, 10% fines value and water absorption. The factors involved in the process are moisture content, binder, Ca(OH)₂ dosage, sintering temperature and duration. It was observed that an increase in binder dosage and sintering temperature resulted in aggregates with higher 10% fines value and low water absorption. The properties of aggregates depended on the type of binder used. Aggregate with kaolinite and metakaolin binders resulted in high 10% fines value. The results indicate the potential for manufacturing high quality lightweight aggregate from bottom ash using clay binders.     

Compressive strength and hydration with age of cement pastes containing dune sand powder

This experimental work has focused on studying the possibility of using dune sand powder (DSP) as a part mass addition to Portland cement. Studying the effect of addition dune sand powder on development of compressive strength and hydration with age of cement pastes as a function of water/binder ratio, was varied, on the one hand, the percentage of the dune sand powder (physico-chemical and chemical effect) and on the other, the fineness of dune sand powder (physical effect). In order to understand better the chemical effect (pozzolanic effect) of dune sand powder in cement pastes, we followed the mixtures hydration (50% pure lime + 50% DSP) by X-ray diffraction. These mixtures pastes present a hydraulic setting which is due to the formation of a C–S–H phase (calcium silicate hydrate). The latter is semi-crystallized. This study is a simplified approach to that of the mixtures (80% ordinary Portland cement + 20% DSP), in which the main reaction is the fixing of the lime coming from the cement hydration in the presence of the dune sand powder (pozzolanic reaction), to form calcium silicate hydrate C–S–H semi-crystallized of second generation. The results proved that up to 20% of dune sand powder as Portland cement replacement could be used with a fineness of 4000 cm²/g without affecting adversely the compressive strength. The dune sand powder, despite its crystalline nature, presents a partial pozzolanic reactivity.     

Laboratory investigation of the properties of asphalt concrete mixtures modified with TOP–SBS

Benefits of adding Tall oil pitch (TOP), Styrene-butadiene-styrene (SBS) and TOP + SBS to AC-10 in variant quantities to AC-10 were investigated. Initial research was done to determine the physical properties of asphalt cement and modifiers.Seven asphalt binder formulations were prepared with 8% of TOP; 8 + 3, 8 + 6 and 8 + 9% of TOP + SBS, respectively; 3, 6 and 9% of SBS by total weight of binder. After that, Marshall samples were prepared by using the modified and unmodified asphalt binders.Additionally, compression strength test were done in different conditions to determine water, heat and frost resistance of all Marshall samples.Fatigue life and plastic deformation tests for Marshall samples (for different asphalt mixtures: modified and unmodified) were carried out using PC controlled repeated load indirect tensile test equipment developed at Suleyman Demirel University by Tigdemir (SDU-Asphalt Tester).The results of investigation indicate that asphalt mixture modified by 8% TOP + 6% SBS gives the best results in the tests that were carried out in this study, so that, this modification increases physical and mechanical properties of asphalt binder.     

Strength,durability, and micro-structural properties of concrete made with used-foundry sand (UFS)

This paper presents the design of concrete mixes made with used-foundry (UFS) sand as partial replacement of fine aggregates. Various mechanical properties are evaluated (compressive strength, and split-tensile strength). Durability of the concrete regarding resistance to chloride penetration, and carbonation is also evaluated. Test results indicate that industrial by-products can produce concrete with sufficient strength and durability to replace normal concrete. Compressive strength, and split-tensile strength, was determined at 28, 90 and 365 days along with carbonation and rapid chloride penetration resistance at 90 and 365 days. Comparative strength development of foundry sand mixes in relation to the control mix i.e. mix without foundry sand was observed. The maximum carbonation depth in natural environment, for mixes containing foundry sand never exceeded 2.5 mm at 90 days and 5 mm at 365 days. The RCPT values, as per ASTM C 1202-97, were less than 750 coulombs at 90 days and 500 coulombs at 365 days which comes under very low category. Thereby, indicating effective use of foundry sand as an alternate material, as partial replacement of fine aggregates in concrete. Micro-structural investigations of control mix and mixes with various percentages of foundry sand were also performed using XRD and SEM techniques. The micro-structural investigations shed some light on the nature of variation in strength at the different replacements of fine aggregates with foundry sand, in concrete.     

Evaluation of strain gage lengths for testing limestone and granite aggregate concretes

An experimental program was conducted to determine an appropriate length of strain gage for use in testing limestone and granite aggregate concretes. Variables in the test program included type and size of aggregate, and length of strain gage. Test specimens consisted of concrete cylinders fitted with a mechanical dial gage, and with multiple electrical resistance strain gages ranging from 120 mm (4.7 in.) to 5 mm (0.2 in.) in length. Cylinders were subjected to compression loading. Strains reported by the strain gages were compared to the strains calculated using dial gage readings. Recommendations are given for appropriate length of strain gages to be used with limestone aggregate and granite aggregate concretes.     

Effect of crumb rubber characteristics on crumb rubber modified (CRM) binder viscosity

Asphalt binder viscosity is of great importance during the production process of hot mix asphalt mixture as typically asphalt plants will store binders between 149 °C and 177 °C. SHRP guidelines state that asphalt binder viscosity must not exceed 3 Pa s. Therefore, given the documented increases in asphalt viscosity when modified with crumb rubber modifier (CRM) it is necessary to produce asphalt binder that fulfills the SHRP criteria while not exceeding plant mixing and storing requirements. This paper reports the results of an investigation of the importance of CRM properties on viscosity of CRM binder. Two binder sources were modified at four concentration levels using four different crumb rubber sources; the viscosities of the produced binders were evaluated by AASHTO T 316. Crumb rubber properties were evaluated by elemental analysis using a scanning electron microscope (SEM) and by determination of glass transition temperature (T_g) using a differential scanning calorimeter (DSC). In general, results indicate that processing procedure and tire type plays an important role in the determination of CRM binder viscosity.     

Damage to cement concrete pavements due to exposure to organic compounds in a cold region

Pop-out and disaggregation of aggregate in a 1-year old cement concrete pavement originally mixed with air-entraining (AE) water-reducing agent was observed after the pavement had been exposed to ethylene glycol based snow-melting agent on the surface in the winter. The study used: gas chromatography–mass spectrometry (GC–MS) tests, ¹H Nuclear Magnetic Resonance (NMR) tests, X-ray fluorescence analysis, emission spectral analysis (ICP), elution tests in anion type surfactant solution conducted for mortar and aggregate taken from the cement concrete where pop-out had occurred, as well as samples made by cement paste in the laboratory. Tests of the tensile strength, thermal-stress, and three-dimensional crack analysis by micro-focus computerized tomography (CT) scanner were conducted for specimens (2.5 × 2.5 × 10 cm) taken from the cement concrete where pop-out had occurred and with cement concrete samples made in the laboratory. Microscope observations and Electron Probe Micro Analyzer (EPMA) analysis were conducted for thin samples (2.5 × 2.5 cm and 20 μm thick) taken from the cement concrete where pop-out had occurred. The tests results showed that organic compounds contained in the cement reacted with the cement during the hardening process, generating cracks and gel in the cement paste. It was established that these caused the pop-out of the aggregate, together with the effects of the ethylene glycol based snow-melting agent that the cement concrete had been exposed to. No pop-out or disaggregation of aggregate were found in cement concrete at a repaired section, at the same location, with aggregate of low absorbing water ratio in this cold region and in place for 2 years.     

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.     

Hybrid effect of carbon nanotube and nano-clay on physico-mechanical properties of cement mortar

In this work, several nanomaterials have been used in cementitious matrices: multi wall carbon nanotubes (MWCNTs) and nano-clays. The physico-mechanical behavior of these nanomaterials and ordinary Portland cement (OPC) was studied. The nano-clay used in this investigation was nano-kaolin. The metakaolin was prepared by thermal activation of nano-kaolin clay at 750 °C for 2 h. The organic ammonium chloride was used to aid in the exfoliation of the clay platelets. The blended cement used in this investigation consists of ordinary Portland cement, carbon nanotubes and exfoliated nano metakaolin. The OPC was substituted by 6 wt.% of cement by nano metakaolin (NMK) and the carbon nanotube was added by ratios of 0.005, 0.02, 0.05 and 0.1 wt.% of cement. The blended cement: sand ratio used in this investigation was 1:2 wt.%. The blended cement mortar was prepared using water/binder ratio of 0.5 wt.% of cement. The fresh mortar pastes were first cured at 100% relative humidity for 24 h and then cured in water for 28 days. Compressive strength, phase composition and microstructure of blended cement were investigated. The results showed that, the replacement of OPC by 6 wt.% NMK increases the compressive strength of blended mortar by 18% compared to control mix and the combination of 6 wt.% NMK and 0.02 wt.% CNTs increased the compressive strength by 29% than control.     

Determining the specific gravities of coarse aggregates utilizing vacuum saturation approach

The current method of specific gravity and absorption of coarse aggregate testing is based on the AASHTO T 85 and ASTM C-127 standards. This approach involves the soaking of the coarse aggregate samples for 15h (AASHTO T 85) and 24 ± 4 h (ASTM C-127), and drying the aggregate to its saturated-surface dry (SSD) state with the aid of a dry absorbent cloth. The attainment of the SSD condition of the coarse aggregate is very subjective, and the total test duration makes it inconvenient for use in construction quality control and quality assurance testing (QC/QA).The objective of this paper is to determine the specific gravity and absorption of coarse aggregates using a new proposed approach utilizing vacuum saturation. In lieu of the conventional soaking period of 24 ± 4 h, this proposed research approach employs the use of 10, 20 and 30 min of vacuum saturation at 30 mm Hg (4.0 kPa) pressure. In this paper, the soaking time is 24 ± 4 h for all the AASHTO method. It is also believed that the 24 ± 4 h shall give better soaking and therefore more accurate test results would be achieved. Vacuum saturating the coarse aggregates aims at removing all the entrapped air within the sample mass, in addition to forcing water into the effective pores of the coarse aggregates. This method is applied to a wide range of coarse aggregates including trap rock, limestone, gravel, steel slag, crushed concrete, and the results are compared statistically with those of AASHTO T 85. Results from the experiments indicate that the vacuum saturation method can replace the AASHTO T 85 for coarse aggregate specific gravity testing at 10, 20 or 30 min of vacuum saturation. A significant finding was that the AASHTO T 85 underestimates the full absorption potential of highly absorptive aggregates when compared to this proposed vacuum saturation approach.     

Prediction of bituminous mixture fatigue life based on accumulated strain

This research was aimed to predict the number of cycles that cause fracture of hot-mix asphalt (HMA) based on the number of cycles at which the slope of accumulated strain switched from decreasing to increasing mode. In addition, the effect of aggregate gradation and temperature on fatigue behaviors of HMA were evaluated.HMA specimens were prepared at optimum asphalt content using the Marshall mix design procedure. The specimens were prepared using crushed limestone aggregate, 60/70 penetration asphalt, and three different aggregate gradations with maximum nominal aggregate size of 12.5, 19.0, and 25.0 mm. Five magnitudes of load (1.5, 2.0, 2.5, 3.0, and 3.5 kN) were evaluated for their effect on fatigue behavior.Constant stress fatigue tests were performed using the Universal Testing Machine (UTM) at 25 °C. Other temperatures (10, 45, and 60 °C) were evaluated at a load of 3.5 kN.The tests results indicated that the slope of accumulated strain continued to decrease until the number of loading cycles approached 44% of the number of cycles that caused fracture of the HMA. Also, the initial stiffness of asphalt mixtures was found to increase as the magnitude of the load applied increased and as the aggregate gradation maximum nominal size decreased.     

Properties of compressed lateritic soil stabilized with a burnt clay–lime binder: Effect of mixture components

In this study, a pozzolanic binder containing lime and a common thermally activated kaolinitic clay, at 750 °C, was formulated. The chemical, mineralogical and pozzolanic properties of raw materials were determined. The percentage of lime in the binder varies between 20% and 30%. The binder was used as a stabilizer in compressed lateritic soil in which water–solid (laterite and binder) and laterite–binder ratios vary, respectively, from 0.12 to 0.20 and 4 to 9. Sodium hydroxide (NaOH) was added as a chemical activator in the mixture. The NaOH–binder ratio varies from 0.02 to 0.04. The average effect of each component of the mixture on compressive strength, water absorption and apparent density of compressed laterite after 7 or 28 days of conservation at 40 ± 1 °C in an atmosphere saturated with water vapour was evaluated in a screening design of the “design in graeco – latin squares” type. It was observed that water–solid and laterite–binder ratios are the factors that influence more the properties of the products. Compressive strength increases up to a water–solid ratio of 0.16 then decreases for higher ratios. Compressive strength decreases with the increase of laterite–binder ratio. Water absorption decreases with the increase of water–solid ratio up to 0.16 then sharply increases for higher ratios. However, water absorption decreases slightly with the increase in the lime content of the binder and sodium hydroxide–binder ratio. The maximum apparent density is observed at water–solid ratio of 0.16. It increases when sodium hydroxide–binder and laterite–binder ratios increase.     

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.     

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.