Anti-vibration characteristics of rubberised reinforced concrete beams

The flexural and vibration properties were examined in order to evaluate the anti-vibration characteristics of rubber modified reinforced concrete beam. The rubberised mixtures were produced by replacing 5, 7.5, and 10 % by mass of the fine aggregate with 1–4 mm scrap truck tyre crumb rubber particles. A series of reinforced concrete beam (1,200 × 135 × 90 mm³) was tested in a free vibration mode and then subsequently in a four point flexural tests. The input and output signals from vibration tests were utilised to calculate various dynamic parameters such as natural frequencies, frequency response function, dynamic modulus of elasticity and damping ratio. The results showed that compared to control mixture, gradual reductions of natural frequencies in first six modes of all rubberised beams with the highest being in the mixture with 10 % rubber contents. In addition, despite the reduction in overall strength, rubberised mixtures showed flexibility under loading due to the higher energy absorption capacity of rubber particles. Compared to control mixture, the results also showed a uniform global decrease in the dynamic modulus over the span. The reduction was found as high as 26 % in the mixture with 10 % rubber content. The results indicated that the rubberised concrete exhibits better anti-vibration properties and could be a viable alternative to use as vibration attenuation material where resistance to impact or blast is required such as in railway buffers, jersey barriers (a protective concrete barrier used as a highway divider and a means of preventing access to a prohibited area) and bunkers.     

Post-fire mechanical performance of concrete made with selected plastic waste aggregates

This paper presents an experimental study about the effects of elevated temperatures on the residual mechanical properties of concrete incorporating selected plastic waste aggregates (PWAs). Six different concrete mixes were prepared: a reference concrete (RC) made with natural aggregates (NAs) and five concrete mixes with replacement ratios of 7.5% and 15% of natural aggregate by three types of polyethylene terephthalate (PET) plastic waste aggregate (CPWA). Specimens were exposed to temperatures of 600 °C and 800 °C for a period of 1 h, after being heated in accordance with the ISO 834 time–temperature curve. After cooling down to ambient temperature, the following properties were evaluated and compared with reference values obtained prior to fire exposure: (i) compressive and (ii) splitting tensile strengths, (iii) elastic modulus, (iv) ultrasonic pulse velocity (UPV), (v) surface hardness, and (vi) water absorption by immersion. For the replacement ratios used in these experiments, the maximum temperatures reached in CPWA were higher than those measured in RC, due to the higher porosity increase with temperature of the former type of concrete that facilitated the propagation of heat inside concrete, and the exothermic thermal decomposition of plastic aggregates that generated additional heat. After exposure to elevated temperatures, the degradation of compressive strength and elastic modulus of CPWA was higher than that of RC, particularly for the highest replacement ratio, as a consequence of the higher porosity increase experienced by CPWA. The reduction of residual splitting tensile strength of CPWA was found to be similar to that of RC, possibly because the incorporation of PWA led to lower internal stresses due to thermal gradients and allowed an easier dispersion of gases confined in pores, thus reducing crack development in the matrix. The magnitude of the degradation of concrete’s residual mechanical properties was seen to depend on the type of PWAs and the replacement ratio. The residual compressive strength of CPWA proved to be strongly correlated with both UPV and water absorption by immersion, but its correlation with surface hardness was less significant.     

Thermal conductivity of ternary mixtures for concrete pavements

This study used a standard procedure to measure the thermal conductivity of ternary concrete mixtures and investigated several factors influencing thermal conductivity. Three different coarse aggregates (Kentucky limestone, Mexican limestone, and river gravel) were used for the concrete mixtures. The measured thermal conductivity of concrete is significantly affected by the type and percentage of coarse aggregate, and moisture content. This finding was confirmed statistically by an Analysis of Variance (ANOVA) method. To understand the effect of supplementary cementitious materials (SCMs), the thermal conductivity of the control and ternary mixtures were measured and provided for use in Portland cement concrete (PCC) pavement design. The thermal conductivity of ternary mixtures increased by 7-10% due to an increase of 1% in moisture. The study developed a model equation that predicts the thermal conductivity of concrete as a function of moisture content and coarse aggregate percentage.     

The effect of superplasticizers on the mechanical performance of concrete made with fine recycled concrete aggregates

It is considered that using crushed recycled concrete as aggregate for concrete production is a viable alternative to dumping and would help to conserve abiotic resources. This use has fundamentally been based on the coarse fraction because the fine fraction is likely to degrade the performance of the resulting concrete. This paper presents results from a research work undertaken at Instituto Superior Técnico (IST), Lisbon, Portugal, in which the effects of incorporating two types of superplasticizer on the mechanical performance of concrete containing fine recycled aggregate were evaluated. The purpose was to see if the addition of superplasticizer would offset the detrimental effects associated with the use of fine recycled concrete aggregate.The experimental programme is described and the results of tests for splitting tensile strength, modulus of elasticity and abrasion resistance are presented. The relative performance of concrete made with recycled aggregate was found to decrease. However, the same concrete with admixtures in general exhibited a better mechanical performance than the reference mixes without admixtures or with a less active superplasticizer. Therefore, it is argued that the mechanical performance of concrete made with fine recycled concrete aggregates can be as good as that of conventional concrete, if superplasticizers are used to reduce the water–cement ratio of the former concrete.     

Transcrystalline morphology and mechanical properties in polypropylene composites containing cellulose treated with sodium hydroxide and cellulase

To evaluate the transcrystalline effects caused by various fibers, which were untreated, or treated with sodium hydroxide and cellulase, isothermal crystallization was performed. It was observed that the untreated and cellulase-treated cellulose fibers (cellulose I) had a nucleating ability to transcrystallize at PP matrix. Especially, cellulose fibers treated with Sodium hydroxide (cellulose II) transcystallized at PP matrix. This result was different from other's. Cellulose fibers also transcrystallized at PP/MAH-PP matrix irrespective of the type of cellulose crystalline structure. In PP/MAH-PP/CELL system, MAH-PP was located around the fiber surface at initial crystallization time, but was gradually expelled from that with the increase of crystallization time, and existed at outer boundaries of transcrstalline region at the final crystallization time. These phenomena were confirmed by IR-IRS spectra. The tensile strength of PP/CELL and PP/MAH-PP/CELL composites decreased with the increase of isothermal crystallization time. Therefore, it is thought that transcrystallinity gives rise to negative effect of tensile strength.     

Stress curves and mechanical properties of high performance concrete

Abstract

In this research, high performance concrete (HPC) was designed by the minimum void ratio method, and slag and silica fumes partially replaced cement, as well as fly ash replacing about 15% of sand. Stress curves for compressive, splitting and flexure strengths of HPC specimens were measured and indicated the experimental concretes had better pastes to void ratios than control batches ratio N=V_p /V_v =1.3. The result indicates that pozzolanic materials provide not only a chemical strength effect, but also a physical packing effect. The compressive stress curves may keep growing as the concrete ages.     

Reactions of cumene hydroperoxide mixed with sodium hydroxide

Decomposition of cumene hydroperoxide (CHP) was undertaken in a free radical chain reaction. The peroxyl group is very active and unstable, while the remainder of the molecule is inert. CHP reacted with various concentrations of dilute sodium hydroxide as a catalyst to cleave at ambient and decomposition temperature. The products were verified by GC/MS, and were quantitatively analyzed by chromatography. CHP cleaved heterolytic with NaOH at 250 degrees C, whose major product was dimethylphenyl carbinol (DMPC); however, the main products become acetophenone and alpha-methylstyrene by cleaved homolytic pathway. The catalytic concentrations of NaOH significantly affected the branch ratios of DMPC under decomposition. Based on the experimental results, a radical cleavage mechanism was proposed. To sum up, the reaction parameters, such as temperature, Lewis base, etc., could affect the incompatibilities and decomposition pathways for proper CHP cleavage process. In addition, exothermic onset temperatures (T0) and heat of decomposition (Delta Hd) of incompatible mixtures and CHP itself were studied by differential scanning calorimetry (DSC). Comparisons of T0, Delta Hd and peak power were assessed to corroborate the severity of thermal hazards. From the decay rate of CHP concentration, the reaction order was determined to be 0.5, and the Arrhenius parameters were measured as Ea=92.1 kJ/mol and frequency factor A=2.42 x 10(10)min(-1).     

Improved method of considering air void and asphalt content changes on long-term performance of asphalt concrete pavements

Mixture properties (aggregate gradation and volumetric quantities), rate of loading and environmental conditions are the most important factors that affect the |E*| values. The main objective of this study was to develop a rational approach to investigate and model the effect of air voids and asphalt content on the |E*| master curves and consequently predict pavement performance. In this study, |E*| tests were conducted on three asphalt concrete mixtures with the same aggregate gradation, but different binder grades. For each of these mixtures, the air void and asphalt contents were varied at three levels. It is found that the developed method provides a more accurate estimate of the effects of volumetric changes in hot mix asphalt. The application of the proposed approach would be most beneficial for quality control/quality assurance purposes, performance-related specifications and for estimating contractors' incentives and penalties, where |E*| is utilised to predict the pavement performance.     

Effects of deicers on the performance of concrete pavements containing air-cooled blast furnace slag and supplementary cementitious materials

This study investigates the effects of continuous deicer exposure on the performance of pavement concretes. For this purpose, the differences in the compressive strength, the changes in the dynamic modulus of elasticity (DME) and the depth of chloride ingress were evaluated during and after the exposure period. Eight different concrete mixtures containing two types of coarse aggregates (i.e. air-cooled blast furnace slag (ACBFS) and natural dolomite) and four types of binder systems (i.e. plain Type I ordinary portland cement (OPC) and three combinations of OPC with fly ash (FA) and/or slag cement (SC)) were examined. These mixtures were exposed to three types of deicers (i.e. MgCl₂, CaCl₂, and NaCl) combined with two different exposure conditions (i.e. freezing-thawing (FT) and wetting-drying (WD)). In cold climates, these exposure conditions are the primary durability challenges that promote the physical deterioration of concrete pavements. The results indicated that among the studied deicers, CaCl₂ had the most destructive effect on the tested concretes while NaCl was found to promote the deepest level of chloride ingress yet was shown to have the least damaging impact on concretes. The microstructure evaluation revealed that the mechanism of concrete deterioration due to the deicer exposure involved chemical reactions between the deicers and concrete hydration products. The use of FA or SC as partial replacements for OPC can offset the detrimental effects of both deicers and FT/WD cycles.     

Three-dimensional surface texture of Portland cement concrete pavements containing nanosilica

Pavement surface texture is critical to tire/pavement interaction. Texture characteristics of concrete containing nanosilica pavement surface has not yet been directly investigated, although researchers have found that nanosilica improved pavement friction values and durability. Specimens with various nanosilica content are tested for three-dimensional (3D) texture height maps which are decomposed using discrete wavelet transform for the calculation of 3D texture indices for macrotexture and microtexture. It is found that 3D texture indices increase correspondingly with the increment of nanosilica content. Significant relationship with R ² values between 0.80 and 0.99 is found between various texture indices and nanosilica content. The increased texture amplitude indicates enhanced pavement friction and then safety. The increment of core material volume implies more texture in the core region, which indicates better longevity of texture. The findings of this research agree with the results of other studies that nanosilica increased the abrasion resistance and frictional property of concrete surface.     

Strain energy release rate at interface of concrete overlaid pavements

A new method for calculating energy release rate (ERR) at the interface of concrete overlaid pavements is proposed using crack closure and the nodal force technique. This method transforms a 3D pavement system into a 2D interfacial crack model via a theoretical conversion. The interfacial ERRs of steel fibre-reinforced, roller-compacted, polymer-modified concrete overlay pavement subjected to vehicular load were calculated and compared with the measured interfacial fracture toughness of the bi-material. It was found that the ERRs considerably decrease with the increase in overlay thickness and elastic modulus of foundation. Thin overlays (less than 100 mm) should not be considered in overlay pavement design to avoid interfacial delamination induced by heavy vehicular loading. For a typical overlay pavement system subjected to complex vehicular loads, an interfacial crack suffers mainly from damage due to mode-I, opening, compared to mode-II, sliding, while mode-III, tearing damage is negligible.     

Dynamic analysis of concrete pavements resting on a two-parameter medium

An analysis procedure based on the finite element method is presented to solve moving-load problems of rigid pavements. The algorithm presented considers the dynamic pavement-aircraft interaction effects. The pavement-foundation system is modelled by thin-plate, non-conforming finite elements resting on a two-parameter elastic medium. The moving aircraft loads are represented by masses supported by a spring-dashpot system moving at a specified initial horizontal velocity and acceleration. The accuracy of the finite element program developed is verified by comparing the numerical results of a static problem with the available solution. A parametric study is conducted to determine the effects of the various parameters on the dynamic response of pavements. Emphasis is placed on identifying the influence of fictitious edge and corner forces acting on the plate due to the deformation of the soil medium outside the plate.     

Prediction of stresses in concrete pavements subjected to non-linear gradients

This paper presents a technique for analyzing the residual stresses in concrete pavements subjected to non-linear (stress or strain) gradients throughout the slab thickness. The analysis is separated into two parts. In the first part, an expression is presented for calculating the self equilibrated stresses within a cross-section due to internal restraints (i.e. satisfying equilibrium conditions and continuity of the strain field within the cross-section). These stresses are independent of slab dimensions and boundary conditions. In step two, the stresses due to external restraints (i.e. self-weight and subgrade reaction) are calculated using an equivalent linear temperature gradient obtained from the first part and using existing closed form solutions by Westergaard [Westergaard, H. M., Computation of stresses in concrete roads. In Proc. of the 5th Annual Meeting, Vol. 5, Part I, Highway Research Board, 1926, pp. 90–112] or Bradbury [Bradbury, R. D., Reinforced Concrete Pavements. Wire Reinforcement Institute, Washington D.C., 1947.]. The solution to this step includes slab length and boundary conditions. Total internal stresses due to non-linear gradients are obtained using the superposition principle. The proposed method has been applied to field data from another study for varying temperature profiles within a 24 h period and compared to results from conventional analysis assuming linear gradients. Significant differences were found between the two methods for night-time and early-morning conditions. A linear gradient solution sometimes underestimates tension in the bottom of a slab prior to vehicle loading by a factor of three.     

Investigation of ride comfort limits on urban asphalt concrete pavements

It is well known that pavement distress negatively affects the drivers and passengers of vehicles. Many studies report that foremost among these negative effects is the vibrations that form within the vehicle. Ride comfort depends on the human response to vibration and vehicle response to the road. The goal of this study was to investigate the effect of pavement condition index on ride comfort and to determine the threshold comfort limits for passenger cars on urban asphalt concrete pavements. The pavement condition index (PCI) was determined for pavement sections subject to different surface distress using the PAVER system. Ride (driving) speeds of 20, 30, 40 and 50 km/h were assessed on the same pavement sections to measure vibrational effects inside the vehicle and on the passenger seat. These measurements were then evaluated using the ISO 2631-1 standard in order to determine the a _wz values. Using the logistic regression technique, predictive model that took into account linguistic concepts for estimating ride comfort levels based on PCI values was developed. With the aid of this mathematical model, comfort threshold values were determined for each driving speed within an interval of 0–100 PCI. The study results indicated that increasing driving speed was generally associated with higher PCI comfort thresholds.     

Enhancing the performance of pre-cast concrete blocks by incorporating waste glass – ASR consideration

There is a growing interest of using recycled crushed glass (RCG) as an aggregate in construction materials especially for non-structural applications. Although the recycled crushed glass is able to reduce the water absorption and drying shrinkage in concrete products due to its near to zero water absorption characteristics, the potential detrimental effect of using glass due to alkali–silica reaction (ASR) in cementitious materials is a real concern. The extent of ASR and its effect on concrete paving blocks produced with partial replacement of natural aggregates by crushed glass cullet are investigated in this study. This study is comprised of two parts. The first part quantified the extent of the ASR expansion and determined the adequate amount of mineral admixtures that was needed to reduce the ASR expansion for concrete paving blocks prepared with different recycled crushed glass contents using an accelerated mortar bar test in accordance with ASTM C 1260 (80 °C, 1 N NaOH solution). In the second part, concrete paving blocks were produced using the optimal mix proportion derived in the first part of this study and the corresponding mechanical properties were determined.It was found from the mortar bar test that the incorporation of 25% or less RCG induced negligible ASR expansion after a testing period of 28 days. For mixes with a glass content of higher than 25%, the incorporation of mineral admixtures such as pulverized fuel ash and metakaolin was able to suppress the ASR expansion within the stipulated limit but the results need to be confirmed by other test methods such as the concrete prism test.The study concluded that the optimal mix formulation for utilizing crushed waste glass in concrete paving blocks should contain at least 10% PFA by weight of the total aggregates used.     

Shrinkage performance of Crumb Rubber Concrete (CRC) prepared by water-soaking treatment method for rigid pavements

This investigation deals with the shrinkage properties of rubberised concrete pavement. Arrays of concrete samples were prepared with different water–cement ratios and rubber content. The experimental results revealed that the introduction of rubber into concrete mixes results in the control of shrinkage cracks if the optimised content of rubber is selected. Accordingly, the optimised rubber content was determined based on the mix characteristics, mechanical properties and the results of plastic and drying shrinkage tests. The mechanical strength, toughness, bleeding, plastic shrinkage and drying shrinkage tests were conducted in this experimental program. Analysing the results revealed that the most promising performance results were achieved for samples prepared with the rubber contents of 20% and 25% of fine aggregates, and water–cement ratios of 0.45 and 0.40, respectively.     

Influence of water and temperature on mechanical properties of selected asphalt pavements

One of the main causes of distress in asphalt pavements is water damage. The purpose of this paper is to compare different test methods to evaluate moisture susceptibility. This is of special importance because of the insufficient effectiveness of the test procedures currently used. In this research, experiments were conducted to investigate the effects of water and temperature on mechanical properties of mixtures with different, air void content. The evaluation of such properties concentrates on the following three approaches: innovative (Coaxial Shear Test), traditional, (Indirect Tensile Test) and empirical (Cantabro Test). Specimens were prepared by means of Superpave Gyratory Compactor (SGC) and divided in two different subsets for controlled dry and wet conditioned testing. Test results indicated that the Indirect Tensile Test (IDT) is not able to discriminate between wet and dry condition as the Coaxial Shear Test (CAST) does. The CAST method reproduces closest the real field conditions and indicates clearly the risk of water damage for open graded mixtures (high air void content). Dense graded mixtures (low air void content) showed less influence probably due to the reduced amount of penetrating water. Cantabro Tests (CAT) provided also significant results in good correlation with air void content and material properties of asphalt mixes.     

Effects of mechanical properties of concrete constituents including active mineral admixtures on fatigue behaviours of high performance concrete

In order to explore the links between the macroscopic and microstructural characteristics of concrete with admixtures of active mineral additions, four series of concrete prisms, of mortar matrix prisms and mortar-aggregate Interfacial Transition Zone (ITZ) are prepared and tested under monotonic and cyclic loads. Five static mechanical parameters (compressive and bending strength, fracture energy, elastic modulus, Poisson ratio) and bending fatigue performance (fatigue life, critical maximum displacement and strain, fatigue damage) of such materials are experimentally evaluated. The results show that degradation laws of concrete properties under both monotonic and cyclic loads vary with the different cohesive strength ratio and elastic modulus ratio of ITZ and mortar matrix. The single or double additions of ground slag and fly ash with optimized mass fractions remarkably enhance the static and bending fatigue properties as well as change the failure mechanisms of concrete.     

Durability performance of concrete made with fine recycled concrete aggregates

Fine recycled aggregates are seen as the last choice in recycling for concrete production. Many references quote their detrimental influence on the most important characteristics of concrete: compressive and tensile strength; modulus of elasticity; water absorption; shrinkage; carbonation and chloride penetration. These two last characteristics are fundamental in terms of the long-term durability of reinforced or prestressed concrete. In the experimental research carried out at IST, part of which has already been published, different concrete mixes (with increasing rates of substitution of fine natural aggregates – sand – with fine recycled aggregates from crushed concrete) were prepared and tested. The results were then compared with those for a reference concrete with exactly the same composition and grading curve, but with no recycled aggregates. This paper presents the main results of this research for water absorption by immersion and capillarity, chloride penetration (by means of the chloride migration coefficient), and carbonation resistance, drawing some conclusions on the feasibility of using this type of aggregate in structural concrete, while taking into account any ensuing obvious positive environmental impact.