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.     

Effect of ferrocement confinement on behavior of concrete

In this study, the use of ferrocement as an external confinement to concrete specimens is investigated. The effectiveness of confinement is achieved by comparing the behavior of retrofitted specimens with that of conventional specimens. The primary test variable considered in this study is the concrete compressive strength. All the other parameters, such as size, shape, number of layers of wire mesh, and L/d ratio of the specimens, were kept constant. The sections chosen are circular cylinders with a size of 150 mm × 300 mm and L/d ratio of 6:1. The test results showed that the confined concrete specimens can enhance the ultimate concrete compressive strengths and failure strains.     

Observed and Predicted Behavior of Maipo River Sand

At present, finite-element methods are frequently used in the analysis of geotechnical engineering problems. The selection of an appropriate constitutive law primarily involves balancing simplicity with accuracy. Given that many practitioners still use the hyperbolic model, the adequacy of a modified version of this simplified stress-strain relation-ship to predict the nonlinear behavior of granular soils, is herein examined. Drained triaxial tests were performed on specimens composed of Maipo River sand at different relative densities. These specimens were subjected to different stress-paths in order to an extensive comparison of the measured strains and the predicted values. In addition, laboratory plate-load tests were conducted on rough, circular and strip, surface footings, which were 100-mm in diameter and 60-mm wide, respectively. The testing box, with dimensions 1.05 m × 1.05 m × 0.65 m, was filled with air-dried sand by using a raining apparatus. A field plate-load test performed on dense sandy gravel was also analyzed. From the good agreement achieved between the empirical observations and both the calculated strains and load-settlement relationships, it is concluded that the proposed hyperbolic model predicts with sufficient accuracy the nonlinear response of granular soils in most practical cases, as long as the soil mass is not close to failure.     

Estimating geometrical and mechanical REV based on synthetic rock mass models at Brunswick Mine

This paper uses a case study from Brunswick Mine in Canada to determine a representative elementary volume (REV) of a jointed rock mass in the vicinity of important underground infrastructure. The equivalent geometrical and mechanical property REV sizes were determined based on fracture systems modeling and numerical experiments on a synthetic rock mass. Structural data collected in massive sulphides were used to generate a large fracture system model (FSM), 40 m×40 m×40 m. This FSM was validated and subsequently sampled to procure 40 cubic specimens with a height to width ratio of 2 based on sample width from 0.05 to 10 m. The specimens were introduced into a 3D particle flow code (PFC3D) model to create synthetic rock mass (SRM) samples. The geometrical REV of the rock mass was determined based on the number of fractures in each sampled volume (P₃₀) and the volumetric fracture intensity (P₃₂) of the samples. The mechanical REV was estimated based on the uniaxial compressive strength (UCS) and elastic modulus (E) of the synthetic rock mass samples.The REV size of the rock mass was determined based on a series of statistical tests. The T-test was used to assess whether the means of the samples were statistically different from each other and the F-test to compare the calculated variance. Finally, the coefficient of variation, for the synthetic rock mass geometrical and mechanical properties, was plotted against sample size. For this particular site the estimated geometrical REV size of the rock mass was 3.5 m×3.5 m×7 m, while the mechanical property REV size was 7 m×7 m×14 m. Consequently, for engineering purposes the largest volume (7 m×7 m×14 m) can be considered as the REV size for this rock mass.     

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.     

Influence of fine tailings on polyester mortar properties

The purpose of this study is to examine the basic properties of polyester mortars using a fine tailings (FT) from an abandoned mine as a filler. FT with sizes of 10–69 μm is obtained through the centrifugal separation of tailing (TA), and tested for such basic properties, as particle shape, fineness of size distribution, liquid resin absorption, and heavy metal leaching. Polyester mortars with FT and ground calcium carbonate (GC) are prepared with various filler-(filler + binder) ratios and replacements of GC with FT, and tested for working life, flexural and compressive strengths, and chemical corrosion resistance. As a result, FT has almost the same properties as GC in terms of particle shape, fineness of size and liquid resin absorption. The working life of polyester mortars is prolonged with an increased filler-(filler + binder) ratio and replacement of GC with FT. From the vantagepoint of the strength development of the polyester mortars with FT, it is recommended that the filler-(filler + binder) ratio and replacement of GC with FT should be controlled at 50% or less. Mass and strength changes are generally lower in mortars containing FT than in those containing GC in all chemical solutions.     

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 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.     

Conditioned MSWI ash-slag-mix as a replacement for cement in cement mortar

Fly-ash and scrubber-ash are byproducts of municipal solid waste incinerators (MSWIs) that require further treatment before disposal to avoid polluting soil and groundwater with heavy metals. Recycling scrubber-ash is not feasible because it is extremely difficult to melt this material. In this study, fly-ash and scrubber-ash from MSWI were pre-mixed, then added to fly-ash from foundry sand and vitrified into slag by melting. The amount of that the latter was adjusted to maintain a basicity (CaO/SiO₂) of 1.1. Slag-blended cement mortar (SCM) specimens were molded with 0–40 wt.% cement replaced by slag powder. Toxicity characteristic leaching procedure (TCLP) tests and compressive strength tests were performed. TCLP test results revealed that the concentrations of leached heavy metals were substantially below the regulatory thresholds. Compressive strengths of the SCM specimens were higher than those of the control group after curing for 7 days or longer. Those that had been cured for 28–90 days were about 124–148% stronger in compression than those in the control group. The Pozzolanic reaction accounts for the strengthening effect in the context of the added slag. It is thus feasible to simultaneously recycle MSWI fly-ash, scrubber-ash and fly-ash from foundry sand into useful resources.     

Investigation of the ultimate particle size distribution of a carbonate sand

A series of ring shear tests were conducted to investigate the ultimate particle size distribution of a carbonate sand. The tests were carried out under different stress levels, on three types of specimens: 1) uniformly graded specimens made of dry natural sand 2) remoulded specimens of the crushed sand after first shearing to large strains 3) specimens made of natural sand grains but with the same grading as in (2). The first series of tests on type (1), carried out to very large strains, led to apparently stable gradings, distinct for each stress level. Only limited additional particle breakage could be induced by remoulding the specimens after shearing (type (2)) and subjecting them to more shearing. Tests on specimens created at the apparently stable gradings (type (3)) but from the intact sand particles however led to significantly greater breakage. For the three types a stable, fractal grading was achieved. Analyses of the soil particles’ shape showed that the aspect ratio, sphericity and circularity reach a steady value at large strains, in parallel to reaching a stable grading. The mobilized angle of shearing resistance however was not significantly different in the different types of samples, suggesting the final grading dominates the behaviour.     

Influence of model footing diameter and embedded depth on particle size effect in centrifugal bearing capacity tests

The influence of the model footing diameter and embedded depth on the bearing capacity of circular shallow footings was studied by centrifugal model testing in order to determine a model footing size and embedded depth against particle size in a model ground. In the series of 37 tests, the ground was made by river sand whose particle size was adjusted by sieving to a mean particle size of 0.6 mm. The diameter of the model footing and the embedded depth were considered as influential parameters in this study. The diameter of the model footings varied from 5 to 40 mm and the ratio of the footing diameter to the mean particle size was calculated as 8.3–66.7. The ratio of the embedded depth to the footing diameter was 0, 0.5 and 1.0. As a result, the bearing capacity in the same equivalent diameter of footing was not dependent on the diameter of model footing when the ratio of footing diameter to particle size is more than 50 with any ratio of embedded depth to footing diameter. Our results that the proposed relationship between the ratio of footing diameter to the particle size and the ratio of the embedded depth to the footing diameter can be used to choose a reasonable model footing diameter, embedded depth and the particle size of ground material for centrifugal model tests.     

Influence of aggregate and curing regime on the mechanical properties of ultra-high performance fibre reinforced concrete (UHPFRC)

A new generation of concrete, ultra-high performance fibre reinforced concrete (UHPFRC) has been developed for its outstanding mechanical performance and shows a very promising future in construction applications. In this paper, several possibilities are examined for reducing the price of producing UHPFRC and for bringing UHPFRC away from solely precast applications and onto the construction site as an in situ material. Recycled glass cullet and two types of local natural sand were examined as replacement materials for the more expensive silica sand normally used to produce UHPFRC. In addition, curing of UHPFRC cubes and prisms at 20 °C and 90 °C has been investigated to determine differences in both mechanical and ductility.The results showed that using more angular sand particles reduces the flowability of fresh UHPFRC. The local natural sand can produce a similar mechanical and ductility of UHPFRC to the silica sand. However the use of Recycled Glass Cullet (RGC) gives approximately 15% lower performance, i.e. flexural strength, compressive strength and fracture energy. Specimens cured at 20 °C give approximately 20% lower compressive strength, 10% lower flexural strength and 15% lower fracture energy than specimens cured at 90 °C from 1 to 7 days.     

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.     

The inter-particle coefficient of friction at the contacts of Leighton Buzzard sand quartz minerals

A series of micro-mechanical tests was carried out in order to investigate the inter-particle coefficient of friction at the contacts of quartz minerals of Leighton Buzzard sand. For this purpose, a custom-built inter-particle loading apparatus was designed and constructed, the main features of which are described briefly in this paper. This apparatus is capable of performing shearing tests at the contacts of soil minerals of a particle–particle type in the range of very small displacements, from less than 1 μm to about 300 μm, and very small normal loads, between about less than 1 N and 15 N. The laboratory data showed that the effects of the normal force and the sliding velocity on the coefficient of dynamic friction are not significant, while dry and saturated surfaces had similar frictional characteristics. The steady state sliding was mobilized within a range of 0.5–3.0 μm of horizontal displacement, and the coefficient of static friction was very similar to the corresponding coefficient during constant shearing. Repeating the inter-particle shearing tests on the same particles and following the same shearing track indicated a small reduction in the inter-particle coefficient of friction after the first shearing, which is possibly related to plastic deformation and damage to the asperities.     

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.     

Numerical simulation of a jointed rock block mechanical behavior adjacent to an underground excavation and comparison with physical model test results

Mechanical behavior of a jointed rock mass with non-persistent joints located adjacent to a free surface on the wall of an excavation was simulated under without and with support stress on the free surface using approximately 0.5 m cubical synthetic jointed rock blocks having 9 non-persistent joints of length 0.5 m, width 0.1 m and a certain orientation arranged in an en echelon and a symmetrical pattern using PFC^3D software package. The joint orientation was changed from one block to another to study the effect of joint orientation on strength, deformability and failure modes of the jointed blocks. First the micro-mechanical parameters of the PFC^3D model were calibrated using the macro mechanical properties of the synthetic intact standard cylindrical specimens and macro mechanical properties of a limited number of physical experiments performed on synthetic jointed rock blocks of approximately 0.5 m cubes. Under no support stress, the synthetic jointed rock blocks exhibited the same three failure modes: (a) intact rock failure, (b) step-path failure and (c) planar failure under both physical experiments and numerical simulations for different orientations. The jointed blocks which failed under intact rock failure mode and planar or step-path failure mode produced high and low jointed block strengths, respectively. Three phases of convergence of free surface were discovered. The joint orientation and support stress played important roles on convergence magnitude. The average increment of jointed block strength turned out to be about 10, 7.9 and 6.6 times the support stress when support stresses of 0.06 MPa, 0.20 MPa and 0.40 MPa were applied, respectively. The modeling results offer some guideline in support design for underground excavations.     

Improvement of residual compressive strength and spalling resistance of high-strength RC columns subjected to fire

This paper investigates the spalling properties of high-strength concrete in order to improve the residual compressive strength and spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from spalling. One specimen, finished by a fire endurance spray, exhibited even more severe spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.     

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.     

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.     

Behavior of FRP-confined concrete after high temperature exposure

This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase experimental program was conducted. In the first phase, 42 standard 100 × 200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high temperature exposure, specimens were tested under uniaxial compression till failure. The test results demonstrated that at a temperature of 100 °C (a little more than the glass transition temperature (T_g) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100 × 100 × 650 mm concrete prisms were prepared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens.