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•Possibility of using recycled HDPE in building materials.•Composite mortars containing HDPE sand can be up to 25% lighter than ordinary mortars.•The thermal conductivity of composite ...LWCM60 may be up to 41% lower than that of NCM.•The modulus of dynamic elasticity of HDPE-based composites is 73% lower.•It is possible to make flexible and shock-resistant cementitious materials.
Today, a large number of research projects are concerned with the recycling of plastic waste to be reused in the field of construction. This work, which is part of a research programme, focuses on the valorization of plastic waste from high density polyethylene (HDPE) pipes, to be used as aggregates. The HDPE aggregates were used as partial replacements of natural sand at 0, 15, 30, 45 and 60%, for the same volume. Only one particle size of the HDPE aggregates was used in each composition of the lightweight composite mortars (LWCM). Prismatic specimens 4 × 4 × 16 cm3 were prepared with a ratio W/C = 0.5. The density of the composite mortars was measured in the fresh and cured states. The compressive and flexural strengths, the thermo-physical characteristics as well as the ultrasonic pulse velocity (UPV) and the dynamic modulus of elasticity (Ed) were also investigated. In addition, composite mortars were analysed using a Scanning Electronic Microscope (SEM). Laboratory tests revealed encouraging results. Compared to the normal composite mortar (NMC), outcomes showed that composite mortar with 60% HDPE aggregates (LWCM60) increased ductility and reduced by 73% the dynamic modulus of elasticity. Analyses using SEM indicated that HDPE aggregates exhibited low adhesion to the cementitious matrix and mortars with higher HDPE rates improved the energy performance of composite mortars (LWCM).
•A standard dense concrete mixture and four pervious concrete mixtures were studied.•A higher amount of small aggregate fractions yielded higher density mixtures.•A higher amount of small aggregate ...fractions yielded greater flexural strength.•Connected porosity was influenced more by the aggregate type than the size.•Pervious concrete can be used as concrete block paving.
This study investigates the influence of aggregate type and size on the properties of pervious concrete. Five different concrete mixtures were prepared, including a standard dense concrete mixture and four pervious concrete mixtures with varied aggregate types (dolomite or steel slag) and differing proportions of 4–8mm to 8–16mm aggregate fractions (30:60 or 60:30). The results suggest that a higher amount of small aggregate fractions (4–8mm) yielded higher density concrete mixtures and greater flexural strength. However, connected porosity as a main parameter for estimating pervious concrete efficiency was surprisingly influenced more by the aggregate type than the size.
•The influence of damage degree on the degradation of concrete under freezing-thawing cycles was systematically investigated.•The mass loss, relative dynamic modulus of elasticity of degraded ...concrete were measured.•The uniaxial compression tests was conducted and stress–strain curves were obtained.•The degradation mechanism of damaged concrete under freezing-thawing cycles was discussed.
The existed studies about the freezing-thawing degradation of concrete mainly focused on non-damaged concrete. This may overestimate the service life of concrete structures. In this paper, the influence of damage degree on the degradation of concrete under freezing-thawing cycles was systematically investigated. The concrete specimens with three different damage degrees (0, 10%, and 20%) of D0, D1, and D2 were prepared. After many freezing-thawing cycles, the mass loss, relative dynamic modulus of elasticity were measured and uniaxial compression tests were conducted. Test results show that the mass of D0 continuously increases with the freezing-thawing cycles before 32, but the mass of D1 and D2 specimens show a negative increase after 16 cycles. The relative dynamic elastic modulus of D1, D2, and D3 showed a decreasing trend. The degradation rate of compressive strength is close to the no-damage concrete when the damage degree is less than 0.1. However, when the damage degree reaches 0.2, the degradation rate of strength accelerates remarkably. The elastic modulus of D0, D1, and D2 specimens decreases linearly with the increase of freezing-thawing cycles. The peak strain varies of D0 specimen change very little before 32 freezing-thawing cycles. For D1 and D2 specimens, the peak strain increases linearly with the increase of freezing-thawing cycles. Finally, the degradation mechanism of concrete with initial damage under the action of freezing-thawing cycles are discussed.
With the continuous increase of infrastructural construction worldwide, the supply of river sand and fresh water for making concrete encountered enormous shortage, especially for coastal regions. To ...alleviate this problem, researchers have started to investigate the possibility of consuming seawater and sea sand as alternatives. This paper reports the results of a comprehensive study on the mechanical and microstructural properties of seawater and sea sand concrete. Three types of concrete: seawater and sea sand concrete (SSC), sea sand concrete (SC), and ordinary concrete (OC), were prepared following two different water/binder ratio. Compressive strength, flexural strength, dynamic modulus of elasticity, and stress-strain relationship as well as microstructural analysis of all the concrete types were investigated. It was observed that the use of seawater and sea sand has led to an increase of the early age compressive strength but slightly decrease of the 28 days strength. The flexural strength of seawater and sea sand concrete, sea sand concrete has been ameliorated at 28 days, when compared, to ordinary concrete. The dynamic modulus of elasticity of concrete made with either seawater and sea sand or sea sand has been significantly enhanced, especially at the early age. X-ray diffraction pattern (XRD) and scanning electron microscopy (SEM) analyses further confirmed that sea sand and seawater have a remarkable effect on the surface morphology and the significant contrast from ordinary concrete due to the dominance of the ettringite phase with crystals that have a fibrous shape, which leads to a compacted and less porous structure and enhancement of the mechanical behavior.
•Two mixes with fly ash and silica fume and three types of concrete were prepared.•Sea sand concrete and seawater and sea sand concrete compressive strength increased up to 23.3% and 15%.•Sea sand concrete and seawater and sea sand concrete has higher Dynamic modulus of elasticity.•Seawater and sea sand are sustainable alternatives for fresh water and river sand in coastal areas.
•Assessment of mechanical and durability properties of rubber ash/fiber concrete.•Addition of rubber fibers in concrete mix increases flexural strength.•Reduction in elastic modulus indicates higher ...flexibility of rubber concrete.•Concrete containing rubber fibers is better in term of abrasion resistance.•Micro-structural study shows weak interfacial bonding.
Now a day’s natural sand is becoming scarcer and costlier due to its non-availability. Waste rubber tire as fine aggregates can be an economical and sustainable alternative to river sand. In this study attempt has been made to utilize waste rubber tire as partial replacement of fine aggregate in the form of rubber ash and rubber ash with rubber fibers (combined form) with three w/c ratios. Workability, compressive strength, flexural strength, density, water absorption, abrasion resistance, carbonation depth, static modulus of elasticity, dynamic modulus of elasticity and chloride ion penetration of rubber ash concrete and modified concrete (10% rubber ash and varied percentage of rubber fibers) have been obtained. Micro-structural study using XRD, EDAX and SEM has also been carried out in this work. It has been shown that flexural strength of rubber ash concrete decreases with the increase of percentage of rubber ash whereas flexural strength of modified concrete is increased with the increase of the percentage of rubber fibers content. The abrasion resistance, carbonation depth, modulus of elasticity and chloride ion penetration of rubber ash concrete and modified concrete were also affected by addition of rubber ash and rubber fibers in concrete.
•RF combined with REF was proposed to predict frost resistance of concrete.•REF helps to identify the key factors of mix proportion influencing frost resistance.•The parameters of the proposed RF ...model were determined to improve predication accuracy.•The applicability of the proposed RF-REF model was verified in the case of diversified mix.
Infrastructure projects in extremely cold areas have high requirements regarding the frost resistance of concrete. To more efficiently design concrete mix proportions in engineering applications to meet the requirements of frost resistance (in terms of the relative dynamic modulus of elasticity after freezing and thawing cycles), an intelligent framework based on the random forest (RF) algorithm is developed to predict the frost resistance of concrete. First, orthogonal tests and engineering data are used to obtain a dataset of raw material mix proportions for concrete and the corresponding frost resistance index values. Second, the RF and recursive feature elimination (RFE) are combined to eliminate coupling factors and noise and determine the optimal factor index system for the concrete mix proportion considering the corresponding influence on frost resistance, and the RF is used to establish a regression prediction function between the concrete mix proportion and frost resistance. Finally, the State Key Project of the Songtong Expressway in Jilin Province is used as a case study to verify the feasibility of the proposed method in a cold region, and the results show that (1) RF-RFE can effectively screen important indicators. After screening, the characteristic parameters are the water binder ratio, cement dosage, coarse aggregate dosage, fine aggregate dosage, compound superplasticizer amount and fly ash dosage. (2) The frost resistance of concrete can be accurately predicted by the RF model. The root mean square error (RMSE) of the test set is 0.077, and the goodness of fit (R2) is 0.9578. The proposed framework can be used to effectively predict the frost resistance of concrete to improve its durability, thus providing a good foundation for the optimization of the concrete mix design in practical engineering and excellent economic benefits and application prospects.
Strength monitoring of early age concrete improves the efficiency of construction as it provides information on the optimum time for shoring removal and pre-stress transferring. Electromechanical ...impedance technique has been proven to be a useful tool for strength monitoring of cementitious materials. One of the key limitations of this technique is the lack of physical models, which resulted in strong reliance on statistical analysis tools to quantify the strength of structure being monitored. In this proof-of-concept study, a novel electromechanical impedance–based model with the potential of monitoring the strength of cementitious materials using the concept of Smart Probe is proposed. Instead of directly bonding a lead zirconate titanate patch on the host structure, a lead zirconate titanate was first surface-bonded on a pre-fabricated aluminum beam, which is termed Smart Probe. The Smart Probe was then partially embedded into cementitious materials for strength monitoring. The structural resonant frequencies of the Smart Probe can be identified from the conductance signatures measured from the lead zirconate titanate patch throughout the curing process and serve as strength indicator. By modeling the cementitious material as an elastic foundation supporting the Smart Probe, an analytical model was developed to predict the dynamic modulus of elasticity of cementitious materials based on the resonance frequency of the Smart Probe. Experimental study was carried out on a mortar slab specimen to verify the model and to investigate the performance of the Smart Probe. It was found that the dynamic modulus of elasticity of the host structure could be predicted from the conductance signatures using the proposed model. Compressive strength assessment was achieved by establishing an empirical relation with the dynamic modulus. The proposed electromechanical impedance–based model with Smart Probe is physically parametric in nature and shows high repeatability, which renders its superiority over the conventional statistical method–based electromechanical impedance technique for strength monitoring of cementitious materials.
Freezing and thawing resistance is a key characteristic for concrete materials in cold weather conditions. In this study, the tensile properties and elastic modulus of ultra-high performance concrete ...(UHPC) under accelerated freeze-thaw cycles are characterized. Six series of UHPC specimens are experimentally tested with a well-designed direct tension test (DTT) method to capture complete tensile stress-strain responses. Both the dynamic and wave moduli of elasticity of UHPC are measured at specific cycles using the standard impact test and self-designed “smart aggregate” technology, respectively. Long term freezing and thawing cyclic conditioning of UHPC samples results in reductions of elastic modulus, tensile strength, strain capacity, and energy absorption capacity. The tensile stress-strain curves of UHPC demonstrate distinct descending with increasing freeze-thaw cycles, particularly in the strain softening region. The energy-based approach is found to be more sensitive and effective than the elastic modulus-based approach when evaluating material deterioration over time and capturing accumulative material degradation subjected to rapidly-repeated freezing and thawing actions. As from the test results, UHPC is characterized as a very durable cementitious material, but it is not inherently unconquerable. Extended freezing and thawing actions can still lead to deterioration of the material, with respect to its elastic modulus, tensile strength, energy absorption capacity, etc. As demonstrated, the DTT method can be used to effectively characterize the long-term performance of UHPC in tension under cold weather conditions.
•B/A ratio affects the physical and mechanical properties of NHL2 and NHL3.5 mortars.•The influence of B/A is different according to the binder type.•20% binder leads to a mortar of lower mechanical ...performance in both cases.•25% binder seems to be the optimum percentage in the case of NHL2.•30% binder seems to be the optimum percentage in the case of NHL3.5.
Natural hydraulic lime (NHL) is a material which has received increased interest in the past decade as a binder for the production of mortars. The renewed interest of researchers and builders in natural hydraulic lime is attributed to its enhanced compatibility with many traditional materials, as well as the fact that it is an environmentally friendly material, especially in relation to modern cement. In the present study, two different types of natural hydraulic lime mortars are studied, using NHL2 and NHL3.5 as binder (in accordance to the new classification EN 459-1:2010) and the same river sand, while the influence of different binder to aggregate ratios on mortar characteristics is also investigated. Fresh mortar characteristics are examined immediately after mixing, while hardened mortar characteristics are evaluated at different mortar ages. Specifically, the mechanical performance of the mortars is evaluated through flexural and compressive strength tests, as well as the dynamic modulus of elasticity, which is estimated through ultrasound pulse velocity measurements. Physical performance of the mortars is investigated through the examination of the pore network structure characteristics, via mercury intrusion porosimetry measurements, and through the examination of hygric characteristics, via water absorption tests. The binder to aggregate ratio seems to play an important role in the development of the mechanical and physical characteristics of the mortars, while it influences mortar properties differently according to the type of the binder.
•Wood stiffness of European beech boards is the highest in pure stands.•Board stiffness from mixed stands with oak and pine is not suitable for high-quality timber.•The higher the cambial age, the ...better the dynamic modulus of elasticity (MOEdyn) of boards.
European beech (Fagus sylvatica L.) is the most commonly occurring deciduous tree species in Central Europe. Because of its competitiveness and (morphological) variability, it occurs in different species mixtures. The aim of the present study was to determine whether, and to what extent, the internal wood properties of European beech are affected by species mixture. Logs obtained from 100 beech trees from the low-mountain Spessart region in Germany were sampled and subdivided into five equal groups representing different mixture types: pure beech stands and four beech stands with the following tree species, respectively: Pseudotsuga menziesii, Picea abies, Pinus sylvestris and Quercus petraea. After logging and sawing, the boards were graded according to strength. For this purpose, the dynamic modulus of elasticity (MOEdyn) was determined. The MOEdyn, which is a relevant property for wood quality in the construction sector, was regressed against various independent variables, such as cambial age or mixture type. Relevant differences in wood quality were observed between mixture types. Beech trees in monocultures had the highest stiffness. In particular, species mixture with the light-demanding Quercus petraea or Pinus sylvestris yielded a significant reduction in the stiffness of the beech timber (–10% and –14%, respectively). Therefore, beech glued laminated timber of higher strength classes (≥GL 40c) was not viable using beech from these mixture types. The findings of this study also revealed significant effects of axial board position and cambial age on MOEdyn. The present transformation of forests into mixed forests affects the quality of the wood. Future research should focus on the dependencies between varying growth conditions—also caused by climate change—and wood formation.
