Effect of waste latex paint on concrete

Approximately 20% of paint sold in western countries does not get used for its intended purpose, and in time much of this left-over paint ends up in land-fill as part of the household waste collection, at a significant economic and environmental cost. In New Zealand, a comprehensive product stewardship campaign has been initiated to recover waste paint before it enters the waste stream, while the collaboration amongst a cohort of companies has contributed to utilising waste latex paint in concrete. The objective of this study was to investigate the effects of waste latex paint on concrete, with special focus on a low strength standard 20 MPa concrete mix. It is demonstrated that waste latex paint can improve the workability and durability of concrete, whilst achieving sufficient compressive strength. Phase analysis indicated that the addition of waste latex paint does not affect the concrete hydrates. It was established that concrete with 12 L/m³ of waste latex paint is suitable for use in low strength non-structural concrete.     

A new method of producing high strength oil palm shell lightweight concrete

This paper presents a new method to produce high strength lightweight aggregate concrete (HSLWAC) using an agricultural solid waste, namely oil palm shell (OPS). This method is based on crushing large old OPS. Crushed OPS are hard and have a strong physical bond with hydrated cement paste. The 28 and 56 days compressive strength achieved in this study were about 53 and 56 MPa, respectively. Furthermore, it was observed that it was possible to produce grade 30 OPS concrete without the addition of any cementitious materials. Compared to previous studies, significantly lower cement content was used to produce this grade of concrete. Unlike OPS concrete incorporating uncrushed OPS aggregate, this study found that there is a strong correlation between the short term and 28-day compressive strength.     

Use of calcium carbide residue and bagasse ash mixtures as a new cementitious material in concrete

Calcium carbide residue (CCR) is a by-product of the acetylene gas production and bagasse ash (BA) is a by-product obtained from the burning of bagasse for electricity generation in the sugar industry. The mixture between CCR contains a high proportion of calcium hydroxide, while BA is a pozzolanic material, can produce a pozzolanic reaction, resulting in the products similar to those obtained from the cement hydration process. Thus, it is possible to use a mixture of CCR and BA as a cementitious material to substitute for Portland cement in concrete. The results indicated that concrete made with CCR and BA mixtures and containing 90 kg/m³ of Portland cement gave the compressive strength of 32.7 MPa at 28 days. These results suggested that the use of ground CCR and ground BA mixtures as a binder could reduce Portland cement consumption by up to 70% compared to conventional concrete that requires 300 kg/m³ of Portland cement to achieve the same compressive strength. In addition, the mechanical properties of the alternative concrete including compressive strength, splitting tensile strength, and elastic modulus were similar to that of conventional concrete.     

Enhancement and prediction of modulus of elasticity of palm kernel shell concrete

This paper presents results of an investigation conducted to enhance and predict the modulus of elasticity (MOE) of palm kernel shell concrete (PKSC). Scanning electron microscopic (SEM) analysis on palm kernel shell (PKS) was conducted. Further, the effect of varying sand and PKS contents and mineral admixtures (silica fume and fly ash) on compressive strength and MOE was investigated. The variables include water-to-binder (w/b) and sand-to-cement (s/c) ratios. Nine concrete mixes were prepared, and tests on static and dynamic moduli of elasticity and compressive strength were conducted.     

Effect of curing parameters on CO2 curing of concrete blocks containing recycled aggregates

In this study, a CO₂ curing process was adopted in order to promote rapid strength development of concrete blocks containing recycled aggregates. The influence of several factors associated with the curing conditions on the curing degree and compressive strength of the concrete blocks were investigated, including curing time, temperature, relative humidity, pressure and post-water curing after the pressurized CO₂ curing (PCC) process. In addition a flow-through CO₂ curing (FCC) method at ambient pressure was also used. The results of the PCC experiments showed that, considerable curing degree and compressive strength were attained during the first 2 h of CO₂ curing, and a prolonged curing time yielded slower gains. The variations of temperature from 20 °C to 80 °C and relative humidity from 50% to 80% had limited impacts on PCC; but the effects of CO₂ gas pressure on the curing degree and compressive strength were more pronounced. The post-water curing after pressurized CO₂ curing allowed the concrete blocks to attain further strength gain but its effectiveness was inversely proportional to the CO₂ curing degree already attained. The FCC experimental results indicated that although a lower curing degree and slower strength development at the early age were observed, after 24 h of curing duration, they were comparable to those obtained by the PCC method. To assess the thermal stability of the concrete blocks, the optimum CO₂ curing regime was adopted for preparing the concrete blocks with recycled aggregates, and the CO₂ cured specimens exhibited better fire resistance than the water-cured ones at 800 °C.     

Modification of four point method to measure the concrete electrical resistivity in presence of reinforcing bars

Concrete resistivity is a material characteristic that can be related to its durability, as it indicates the amount and tortuosity of the pore network and also informs on the degree of water saturation. Its measurement is usually made in situ by the use of the four-point or Wenner method, but the accuracy of such measurements is affected by the presence of metallic reinforcement. In those cases, measurements should not be made on the surface immediately above the reinforcing bar. This paper examines the effects of rebar presence/absence on the resistivity measurements and the significance of a rebar presence factor, which is determined by means of numerical simulations using the COMSOL Multiphysics software package. The results indicate that the rebar presence apparently lowers the resistivity values in a proportion which is a function of the specimen geometry and the electrode spacing. Equations for its quantification are presented.     

Effect of a new additive on mechanical properties of hot-pressed silicon carbide ceramics

The mechanical properties and microstructure of SiC ceramics, hot pressed by simultaneously adding nano-SiC and oxides (MgO+Al₂O₃+Y₂O₃) or nitrate salts (Mg(NO₃)₂+Al(NO₃)₃+Y(NO₃)₃) as additives, were evaluated. The oxide additives system slightly influenced the mechanical properties of the ceramics, while the addition of nano-SiC lead to finer microstructure, and 5 vol.% nano-SiC changed the fracture mode from intergranular type to transgranular type. The ceramics with nitrate salts had fine, equiaxed grains with an average grain size larger than that of the system added oxides, thus inducing lower Viker’s hardness and flexural strength, while the presence of crystalline YAG phase improved the fracture toughness by 54.7%. Also, an observed increase in grain growth—with decreasing weight fraction of liquid and the grounded grain morphology in this system—confirmed a diffusion-controlled growth mechanism. Although the sample with the least amount of additives has the lowest relative density and largest grain size, its flexural strength did not drastically decrease. The influence of nano-SiC on the fracture toughness in the nitrate additive system was negligible.     

石屑应用于混凝土中的探索性试验

本文将石屑和水洗河砂按比例配制组成混合砂应用于混凝土中,通过试验调整和试用,混凝土工作性和强度良好。     

Effects of super plasticizer and curing conditions on properties of concrete with and without fiber

In this study, effects of super plasticizer (SP) and curing conditions on properties of concrete with and without fiber were investigated. In the concrete mixtures, Portland cement, artificial aggregate, SP and steel fibers were used. SP in concrete mixtures was used with ratios of 1.0%, 1.5%, and 2.0% by weight of cement and so C25 concrete was produced with and without fiber. Specimens were cured under two different curing conditions being continuous moist curing and open-air curing. Produced concrete with and without fiber were compared with each other as well as with Portland cement concrete. The highest compressive and flexural strength were obtained with 1.0% and 1.5% SP fiber reinforced concrete, respectively.     

Aggregate packing and -void saturation in mortar and concrete proportioning

Proportioning was studied by measuring aggregate packing (C) and filling of aggregate void space (1?C) with varying volumes of cement paste (\(V_{\rm p}\)) or matrix (\(V_{\rm matrix}\)), i.e., all material <0.125 mm. Eleven widely different normal density aggregates with C = 0.57 to 0.71, i.e., aggregate void content (1?C) = 0.29 to 0.43, were used at constant w/c = 0.38 and flowing consistency and varying dosage of water reducer and paste- and matrix volume. Analysing plots of four excess phase volumes (paste with/without air, matrix with/without air) versus aggregate void space showed constant aggregate void saturation ratios. Both paste- and matrix-aggregate void saturation ratio can be used with the best estimate (\(V_{\rm p}-V_{\rm air})/{(1-C)}=1.15\) per \(\hbox{m}^{3}\). Including air voids in paste- or matrix volume improved correlation so air void content must be included in the normalized paste aggregate void saturation ratio (\(k=V_{\rm p}\)/[(1?C) \(V_{\rm tot}\)]). Simple measurements of aggregate packing are thus very useful. Cost per unit material, per unit fresh (slump, flow diameter) or hardened (compressive strength) property were used to show the cost efficiency of the mixes. The ranking of cost/MPa strength and cost/mm consistency is similar to ranking of total concrete cost for the 11 aggregates with a certain scatter though.     

Effect of reinforcements on strength of Mg9%Al composites

Magnesium-based composites reinforced respectively with four types of particulates at different volume fraction were synthesized through powder metallurgy rout. Mechanical properties show that incorporation of TiB₂ particulates leads to a reduction in the yield stress of the composite while use of ZrB₂ and SiC reinforcements enhances mechanical properties. TiC shows less effect on the yield stress of the composite. The strengths of the four composites increase with increasing volume fraction of particulates at initial stage while decrease at high volume fraction. The optimal volume fraction is about 8%.     

Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate

Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of each component are individually considered. The test variables include the mixture proportioning method, and the aggregate type. The results show that the amounts of creep and shrinkage in concretes made with coarse RCA, and proportioned by the new method, are comparable to, or even lower than, those in similar concretes made entirely with natural aggregates. Furthermore, it is demonstrated that by applying the proposed “residual mortar factor” to the existing ACI and CEB methods for calculating creep or shrinkage of conventional concrete, these methods could be also applied to predict the creep and shrinkage of RCA-concrete.     

Microscopic, physical and mechanical analysis of polypropylene fiber reinforced concrete

This investigation examined the reinforcing effects and mechanisms of polypropylene fiber (PF) on the physical and mechanical properties of concrete. Scanning electron microscope (SEM) was used to observe the crystal structures and that at the aggregate-cement interfacial transition zone. Physical and mechanical tests were performed to measure the effects of PF on improving concrete's engineering properties. Results indicate that PF significantly alters the microstructure of concrete, reduces the crystallization and orientation of Ca(OH)₂, and decreases micro-voids. Specifically, PF forms a network that restricts the growth of Ca(OH)₂, bridges cracking, and reallocates stresses. PF has reduced the amount and size of crystalline, and the micro-cracking at the aggregate-cement interfacial transition zone. As a result, PF has effectively improved concrete's compressive strength, flexural strength, bonding strength, dynamic performance, and fatigue life, while reduced the water penetration and abrasion mass loss. Results also indicate that a PF content of 0.9 kg/m³ has the optimum concrete performance output for the materials used in this study.     

Bar-concrete bond in mixes containing calcium carbide residue,fly ash and recycled concrete aggregate

A mixture of calcium carbide residue and fly ash (CRFA) is an innovative new binder for concrete instead of using ordinary Portland cement (OPC). Therefore, this study aims at investigating the bond interaction between common steel reinforcing bars and the aforementioned concrete. To this end, both CRFA and OPC concretes using crushed limestone and recycled concrete aggregate (RCA) as a coarse aggregate were prepared to investigate the bond strength of smooth and deformed bars by pull-out tests. The bond stress−slip relationships were also identified to determine the effects of CRFA binder and RCA on the bond strength behavior. The results indicate that the values the of bond-slip behavior and bond strengths of steel bar in CRFA concretes are similar to those embedded in OPC concrete. Moreover, the bond strength was significantly affected by RCA and the types of steel bar. Although the concretes had the same compressive strengths, the deformed bar embedded in CRFA concrete with RCA had a lower bond strength than the one with crushed limestone. However, the reduction in bond strength of the CRFA concrete with RCA was still less than that of OPC concrete with RCA. For the CRFA concretes, the bond strengths of the deformed bars were approximately 1.7–3.6 times higher than that of smooth bars.     

Effect of aggregate shape on the mechanical properties of a simple concrete

The influence of aggregate shape on the fracture energy, tensile strength and elasticity modulus in concrete is considered. For this purpose, eight simple cement-based composites were designed, manufactured and tested, with two purposes: to provide experimental data that can throw some light on this involved problem and help in the design of future cement-based composites, and supply information that can be used as a benchmark for checking numerical models of concrete failure, as this simple composite is amenable to being modelled quite easily. Thirty-six notched beams were tested and values of the fracture energy and elasticity modulus were recorded. The tensile strength was measured from indirect standard tensile tests. Comparison with available experimental data is also included and discussed. Fracture was modelled using a cohesive crack with a bilinear softening function; data of the softening function inferred from the experimental measurements are also provided and discussed.     

Recommendation of RILEM TC 200-HTC: Mechanical concrete properties at high temperatures—modelling and application

Mechanical concrete properties at high temperatures depend on many parameters. The main parameters are the specimen type and the test conditions. The report describes the test parameters and test procedures for relaxation tests in the range of 20 to 750°C. TC Membership: The draft of this document has been prepared by the following 16 Committee full members representing 12 countries. Chairman: U. Schneider, Austria; Secretary: R. Felicetti, Italy. Members: G. Debicki, France; U. Diederichs, Germany; J.-M. Franssen, Belgium; U.-M. Jumppanen, Finland; G.A. Khoury, UK; S. Leonivich, Republic Belarus; A. Millard, France; W. A. Morris, UK; L. T. Phan, USA; P. Pimienta, France; P. Rodrigues, Portugal; E. Schlangen, The Netherlands; P. Schwesinger, Germany; Y. Zaytsev, Russian Federation.     

Study on reinforced lightweight coconut shell concrete beam behavior under torsion

This research investigates and evaluates the results of coconut shell concrete beams subjected to torsion and compared with conventional concrete beams. Eight beams, four with coconut shell concrete and four with conventional concrete were fabricated and tested. Study includes the general cracking characteristics, pre cracking behavior and analysis, post cracking behavior and analysis, minimum torsional reinforcement, torsional reinforcement, ductility, crack width and stiffness. It was observed that the torsional behavior of coconut shell concrete is comparable to that of conventional concrete. Compare to ACI prediction, equation suggested by Macgregor is more conservative in calculating cracking torsional resistance. But for the calculation of ultimate torque strength ACI prediction is more conservative compared to the equation suggested by Macgregor. Indian standard is also conservative in this regard, but it was under estimated compared to ACI and Macgregor equations. Minimum torsional reinforcement in beams is necessary to ensure that the beam do not fail at cracking. Compared to conventional concrete specimens, coconut shell concrete specimens have more ductility. Crack width at initial cracking torque for both conventional and coconut shell concrete with corresponding reinforcement ratios is almost similar.     

On the reinforcement of concrete sleepers by composite materials

The most important role of sleepers in a railroad system is conveyance of the train load from rail to the ballast. Since the sleepers are under complicated loading in real conditions, the first stage is static analysis of them. Future railway traffic will certainly be even faster than that of today, and at the same time the demanded load capacity of the trains will probably increase. This implies that the demands for concrete sleepers will increase and the need for reliable analytical tools will be extensive in the near future.

The aim of this work is to increase the load capacity of the sleepers by means of composite materials and to make the railroad system ready for heavier and faster trains. The first step is applying a closed form solution. Then a finite element model of a concrete sleeper is established, in the nest step. Later a full-scale test of reinforced and non-reinforced sleepers is done, and at last, a validation of the finite element model through comparison with full-scale test results as well as closed form solution is conducted. The percentage of increased load capacity of sleepers and good agreements between the results make the work beneficial and reliable.     

Effect of different curing systems on the mechanical and physico-chemical properties of acrylonitrile butadiene rubber vulcanizates

In the present study, the effect of different curing systems including sulfur, dicumyl peroxide, dicumyl peroxide/coagent and radiation/coagent on the mechanical and physico-chemical properties of acrylonitrile butadiene rubber (NBR) was studied. In order to correlate, the effect of curing systems on rubber, the comparison was carried out at comparable value of volume fraction of rubber in swollen gel (V_r) for NBR vulcanizates. Mechanical properties like tensile strength, elongation at break, modulus, Young’s modulus, tearing strength and abrasion loss of vulcanizates have been followed up for comparison. In addition, physico-chemical properties like swelling ratio, soluble fraction, and cross-link density were investigated. On the other hand, the effects of fuel, thermogravimetric analysis, and thermal ageing have been studied.     

Application of 3D-DIC to characterize the effect of aggregate size and volume on non-uniform shrinkage strain distribution in concrete

To elucidate the effect of aggregate size and volume on the non-uniform strain distribution in concrete, drying shrinkage of mortar and concretes were determined with 3D digital image correlation (3D-DIC). The distribution of shrinkage displacements and strains in mortar and concrete were analyzed. The results show that 3D-DIC makes it possible to measure non-uniform displacement distributions initiated by shrinkage in mortar and concrete. The non-uniformity became more remarkable with drying time. The presence of aggregates larger than 5 mm in concrete have locally changed the displacement and strain fields. Aggregates within 5–25 mm make non-uniform strain of concrete more fluctuant, especially when the aggregate size is larger than 10 mm. The maximum and minimum principal strain distributions became more heterogeneous with decreasing volume of aggregates.