Reuse of incineration fly ashes and reaction ashes for manufacturing lightweight aggregate

This paper reports the result of the investigation on manufacturing lightweight aggregate by incorporating municipal solid waste (MSW) incineration fly ashes and reaction ashes with reservoir sediments. The investigation was first performed in a laboratory scale to assess the effects of the composition and the firing conditions on the properties of the resulting aggregate. Afterward, a big amount of aggregates was manufactured in a pilot scale using a commercially available rotary kiln. Physical properties of the synthetic aggregates were subsequently assessed. In addition, compressive strength of the concrete made from the manufactured aggregates was experimentally measured. The investigation shows that the analysis results for the MSW incineration fly ashes and reaction ashes are not in the limits of the expandable region of Riley’s ternary diagram due to the low content of SiO₂. Therefore, they can only be used as additives. The proper content for MSW incineration ashes should not exceed 30%, except compositional adjustment using oxide constituents. The particle density of the manufactured aggregates using a commercially available rotary kiln was 0.99 g/cm³, which is significantly lower than normal density aggregate. Moreover, its dry loose bulk density is 593 kg/m³, which meets the requirements of ASTM C 330 with bulk density less than 880 kg/m³ for coarse aggregate. On the other hand, the results of toxicity test meet the Taiwan Environmental Regulatory requirements, which demonstrate that the aggregate thus fabricated is non-hazardous for construction use.     

Recycled concrete made with different natural coarse aggregates exposed to high temperature

The recycled aggregates obtained from crushed waste concretes have different characteristics from those of natural aggregates. For that reason, the mixture proportions and the fresh and hardened properties of recycled concretes are different. The performance of recycled concrete exposed to high temperatures is not a very well-known subject since most studies have been conducted on conventional concretes. Recycled concretes with water/cement (w/c) ratios of 0.40 and 0.70, and made with three different types of natural coarse aggregate were exposed to 500 °C for 1 h. These concretes were evaluated by the ultrasonic method, resonance frequency, static modulus of elasticity and compressive strength, before and after heating, and compared with those obtained on similar conventional concretes containing the same type of natural coarse aggregate. The conventional and recycled concretes made with quartzitic coarse aggregate performed better after the heat treatment.     

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.     

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.     

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300 °C, 600 °C and 800 °C for 3 h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.     

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.     

Behaviour of recycled aggregate concrete under drop weight impact load

This paper presents the experimental results of recycled aggregate concrete (RAC) beams prepared with different amount of recycled coarse aggregate (RCA) subjected to low velocity impact. The recycled coarse aggregates are obtained from a demolished RCC culvert. Four concrete mixes with 0%, 25%, 50% and 100% RCA respectively are prepared. With each mix three beam specimens of size 1.15 × 0.1 × 0.15 m are prepared and tested under drop weight impact load. The behavior of the RAC beams are studied in terms of acceleration, strains and support reaction histories under impact load in addition to the physical and mechanical characteristics of RCA and RAC. It is observed that 25% RCA does not influence the strength of concrete. In addition, it is found that for a given impact energy (the energy imparted by the hammer per blow) the reactions and strains of RAC with 50% and 100% RCA are significantly lower and higher respectively than those of normal concrete and RAC with 25% RCA.     

Post-fire residual mechanical properties of concrete made with recycled rubber aggregate

This study investigates the effects of elevated temperatures on the residual mechanical performance of concrete produced with recycled rubber aggregate (RRA). Four different concrete compositions were prepared: a reference concrete (RC) made with natural coarse aggregate and three concrete mixes with replacement rates of 5%, 10% and 15% of natural fine and coarse aggregate by RRA from used tyres. Specimens were exposed for a period of 1 h to temperatures of 400 °C, 600 °C and 800 °C, after being heated in accordance with ISO 834 time–temperature curve. After cooling down to ambient temperature, the compressive strength and the splitting tensile strength were evaluated and compared with reference values obtained prior to fire exposure. For the replacement rates used in the present experiments, the obtained results show that concrete made with recycled rubber aggregate (CRRA) present a thermal response that is roughly similar to that of RC; in addition, although residual mechanical properties of CRRA are noticeably more affected than those of RC, particularly for higher exposure temperatures, the relative reduction should not prevent it from being used in structural applications.     

Evaluating Zn,Al and Al–Zn coatings on carbon steel in a special atmosphere

This paper presents a comparative evaluation of Al, Zn and Al–Zn coatings on carbon steel, exposed to a coastal-marine atmosphere. It is a very aggressive atmosphere with high wind velocities (corrosion–erosion rate ≈ 1.4 mm/year (55.12 mpy) for ASTM 1029 steel). Two flame spraying zinc coatings with pore sealers were also evaluated. ISO and ASTM standards were used for the evaluation.After a 2-year exposure the best performance was achieved by the flame spraying Zn/15Al alloy (85% Zn–15%Al) with some damage of the coatings. But the one with a wash primer pore sealer did not show signs of damage.     

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.     

Micro-analysis of the role of interfacial transition zone in “salt weathering” on concrete

When concrete elements are partially immersed in the sulfate environment, researchers always attribute “salt weathering”, “salt crystallization” or “physical attack” to the failure of concrete. However, there were few micro-analysis evidences to support this view. In this paper, an attempt was carried out to study whether salt weathering is really responsible for the concrete damage.As we know, the interfacial transition zone (ITZ) between paste and aggregate plays a determining role in the performance of concrete. In this paper, we focused on the role of ITZ in “salt weathering” on concrete. Concrete specimens, made with coarse aggregate and cement paste, were partially exposed to a 5% sodium sulfate solution and a 5% magnesium sulfate solution respectively, in a controlled environment (20 ± 2 °C, and 60 ± 5% RH). After 8 months of exposure, a micro-analysis is performed by means of XRD, ESEM and EDS. The experimental results showed that, in the upper part of concrete above the Na₂SO₄ solution, damage initiated in the ITZ between paste and aggregate due to the formation of ettringite and gypsum. Salt crystallization cannot occur on the paste surface in the ITZ, but it was found on the aggregate surface after damage initiation due to chemical sulfate attack. On the other hand, salt crystallization could occur in the carbonated concrete. There was no trace of salt crystallization in the concrete partially exposed to MgSO₄ solution.     

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.     

A laboratory study on stone matrix asphalt using ground tire rubber

This research investigated the feasibility using asphalt rubber (AR), produced by blending ground tire rubber (GTR) with an asphalt, as a binder for stone matrix asphalt (SMA). Two different sizes of GTR produced in Taiwan were used. The potential performance of AR–SMA mixtures was also evaluated. The results of this study showed that it was not feasible to produce a suitable SMA mixture using an asphalt rubber made by blending an AC-20 with 30% coarse GTR with a maximum size of 0.85 mm. However, SMA mixtures meeting typical volumetric requirements for SMA could be produced using an asphalt rubber containing 20% of a fine GTR with a maximum size of 0.6 mm. No fiber was needed to prevent drain-down when this asphalt rubber was used. The AR–SMA mixtures were not significantly different from the conventional SMA mixtures in terms of moisture susceptibility from the results of AASHTO T283 tests. The results of the wheel tracking tests at 60 °C show that rutting resistance of AR–SMA mixtures was better than that of the conventional SMA mixtures.     

Concrete building blocks made with recycled demolition aggregate

A study undertaken at the University of Liverpool has investigated the potential for using recycled demolition aggregate in the manufacture of precast concrete building blocks. Recycled aggregates derived from construction and demolition waste (C&DW) can be used to replace quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The manufacturing process used in factories, for large-scale production, involves a “vibro-compaction” casting procedure, using a relatively dry concrete mix with low cement content (≈100 kg/m³). Trials in the laboratory successfully replicated the manufacturing process using a specially modified electric hammer drill to compact the concrete mix into oversize steel moulds to produce blocks of the same physical and mechanical properties as the commercial blocks. This enabled investigations of the effect of partially replacing newly quarried with recycled demolition aggregate on the compressive strength of building blocks to be carried out in the laboratory. Levels of replacement of newly quarried with recycled demolition aggregate have been determined that will not have significant detrimental effect on the mechanical properties. Factory trials showed that there were no practical problems with the use of recycled demolition aggregate in the manufacture of building blocks. The factory strengths obtained confirmed that the replacement levels selected, based on the laboratory work, did not cause any significant strength reduction, i.e. there was no requirement to increase the cement content to maintain the required strength, and therefore there would be no additional cost to the manufacturers if they were to use recycled demolition aggregate for their routine concrete building block production.     

Optimisation of using lightweight aggregates in mitigating autogenous deformation of concrete

Experiments were conducted to determine the effects of using dispersed saturated lightweight aggregates (LWAs) as water reservoirs in mitigating the autogenous deformation of high performance concrete and to establish the optimum solutions as a combination of a number of factors affecting the fracture and mechanical characteristics of concrete. For this purpose, in concretes prepared with a constant low water to cement ratio, normal aggregates were replaced by natural LWAs with size fractions of 2–4 mm or 4–8 mm at three different volume fractions such as 10%, 20% and 30% of the total aggregate volume of concrete. The results indicate that the inclusion of fine fraction of LWAs in concrete reduces the autogenous deformation significantly compared to that of the coarse fraction. It is also shown that concretes with fine fraction of LWAs have enhanced fracture and mechanical properties compared to those with coarse fraction of LWAs. Increasing the replacement ratio of LWAs mitigates autogenous deformation, while having an unfavourable effect on fracture and mechanical properties of concrete for both size replacements. A multi-objective simultaneous optimisation technique, in which the response surface method (RSM) is incorporated, is used to optimise the mitigation ratio of autogenous deformation and fracture parameters of high strength concretes in an effort to obtain a more ductile concrete with less autogenous deformation.     

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.     

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.     

Mechanical and elastic behaviour of concretes made of recycled-concrete coarse aggregates

In this paper an investigation of mechanical behaviour and elastic properties of recycled-aggregate concretes is presented. These concretes were prepared by alternatively using two different (coarse and finer coarse) recycled-aggregate fractions both made of recycled concrete coming from a recycling plant in which rubble from demolition is collected and suitably treated. Several concrete mixtures were prepared by using only virgin aggregates (as reference), 30% finer coarse recycled aggregate replacing fine gravel and 30% coarse recycled aggregate replacing gravel. Five different water to cement ratios were adopted as: 0.40, 0.45, 0.50, 0.55 and 0.60. Concrete workability was in the slump range of 190–200 mm. Compression tests were carried out after 28 days of wet curing. In addition, concrete elastic modulus and drying shrinkage were evaluated. Results obtained showed that structural concrete up to C32/40 strength class can be manufactured by replacing 30% virgin aggregate with recycled-concrete aggregate. Moreover, a correlation between elastic modulus and compressive strength of recycled-aggregate concrete was found and compared to those reported in the literature. Finally, on the basis of drying shrinkage results, particularly if finer coarse recycled-concrete aggregate is added to the mixture, lower strains could be detected especially for earlier curing time.     

Nanostructured zonolite–cementitious surface compounds for thermal insulation

This paper investigates the effect of zonolite loadings on the thermal resistivity and indirect tensile strength of nanostructured cementitious compounds. The main objective of this research is to develop a structural lightweight compound that can be used on building skins and cores for pre fabricated structural insulated panels (SIPs). The application of this compound is intended to improve the thermal resistivity of the building envelope with suitable mechanical performances. The zonolite dosage was added to the cement-nano clay blend at different dosages up to 40% by weight. The nano clay reinforcement used is montmorillonite clay (Hydrated sodium calcium aluminum silicate). The mixes were prepared using water of consistence. The wet compounds were molded in PVC cylindrical molds, having 50 mm inside diameter and 27 mm height, and left for 24 h, then demolded and cured in humid air (20 ± 1 °C&100% RH) for 28 days. The samples were then dried at 105 ± 5 °C for 24 h before testing using a forced convection oven. The thermal resistivity and indirect tensile strength of the different compounds were evaluated. Results demonstrate that the thermal resistivity at 40% zonolite loading enhanced by about 2.9 folds compared to the control samples. An increase of more than 30% in the indirect tensile strength was also achieved when a 0.5% by weight of polycarboxylate superplasticizer was used.     

Use of recycled demolition aggregate in precast products,phase II: Concrete paving blocks

A study undertaken at the University of Liverpool has investigated the potential for using construction and demolition waste (C&DW) as aggregate in the manufacture of a range of precast concrete products, i.e. building and paving blocks and pavement flags. Phase II, which is reported here, investigated concrete paving blocks. Recycled demolition aggregate can be used to replace newly quarried limestone aggregate, usually used in coarse (6 mm) and fine (4 mm-to-dust) gradings. The first objective, as was the case with concrete building blocks, was to replicate the process used by industry in fabricating concrete paving blocks in the laboratory. The compaction technique used involved vibration and pressure at the same time, i.e. a vibro-compaction technique. An electric hammer used previously for building blocks was not sufficient for adequate compaction of paving blocks. Adequate compaction could only be achieved by using the electric hammer while the specimens were on a vibrating table. The experimental work involved two main series of tests, i.e. paving blocks made with concrete- and masonry-derived aggregate. Variables that were investigated were level of replacement of (a) coarse aggregate only, (b) fine aggregate only, and (c) both coarse and fine aggregate. Investigation of mechanical properties, i.e. compressive and tensile splitting strength, of paving blocks made with recycled demolition aggregate determined levels of replacement which produced similar mechanical properties to paving blocks made with newly quarried aggregates. This had to be achieved without an increase in the cement content. The results from this research programme indicate that recycled demolition aggregate can be used for this new higher value market and therefore may encourage demolition contractors to develop crushing and screening facilities for this.