Sets Of Concrete Specimens Research Articles

Development of the recording device to reduce an overlook of a defect for the impact acoustic method

Several concrete structures in Japan built during a period of high economic growth—including bridges (40%) and tunnels (25%)—are now at least 40 years old and are withering. Recent years have witnessed several accidents caused by falling concrete debris from these structures. To ensure safety, these buildings are regularly inspected with non-destructive tests such as the impact acoustic method (IAM). In this method, the surface of the concrete structure under inspection is impacted by a hammer and the resulting sound vibrations are used to detect defects. According to the current inspection standard, inspection records only contain information of detectable defects, because the method relies on the physical capabilities and expertise of the professional. Consequently, there are no records of imperceptible defects. In this study, we developed a recording device that consists of an accelerometer and a microphone and connected it to an impact hammer. The device saves the output from the two components in a single file. A set of concrete specimens were then tested using the IAM with the new device and hammer. Furthermore, the contact time and striking power of the hammer were estimated using a load sensor.

Evaluation of compressive strength of Euphorbia tortilis cactus infused M25 concrete by using ABAQUS under static load

This research presents a novel approach for numerically analyzing concrete with Euphorbia Tortilis Cactus (ETC) to determine its compressive strength. Mesoscale finite element (FE) models were developed, incorporating the mechanical properties of different concrete components. Two sets of concrete specimens with varying ETC content were studied. ABAQUS's explicit dynamics solver was employed for the analysis, and the computed compressive strengths closely matched the experimental data, with deviations of 1.2% and 0.96% (affecting elasticity and strength) for the concrete sets with and without ETC, respectively. The study demonstrates the accuracy and effectiveness of this approach as a quality control tool for concrete constructions, affirming the applicability of ABAQUS for predicting concrete strength.

STUDY ON MECHANICAL PROPERTIES OF HIGH STRENGTH CONCRETE WITH SILICA FUME, FLYASH AND STEEL FIBER

In this growing world there has always been a strong competition in the market amongst industries in term of economy, profits, shares etc. one such industry is construction industry where concrete is the key building substance which is in limelight. Since past, we have seen much advancement in concrete because of the research which is in progress on concrete to come out with a product which should be economical and strong enough to resist all kind of loads. In this thesis, fly ash and silica fume are used as a replacement for cement along with steel fibers by volume of concrete. Here, fly ash is replaced by 0%, 15%, 30% and silica fume is replaced by 0%, 6%, 12% and 18% for cement. Initially, a set of concrete specimens were casted with 0%, 15%, 30% fly ash and 0%, 6%, 12% and 18% silica fume with 0% addition of steel fibers and tested for compressive, flexural and split tensile strength. Secondly, another set of concrete specimens were casted with 0%, 15%, 30% fly ash and 0%, 6%, 12% and 18% silica fume with 0.5% addition of steel fibers and tested for the same. Similarly, another set of samples were casted 0%, 15%, 30% fly ash and 0%, 6%, 12% and 18% silica fume with 1% addition of steel fibers and tested to determine the mechanical properties of concrete. And it was observed that maximum compressive, flexural and split tensile strength was attained at 15% fly ash and 12% silica fume with 1% steel fiber

Fracture behavior and acoustic emission characteristics of reinforced concrete under mixed mode I-II load conditions

In this paper, the fracture behavior and acoustic emission (AE) characteristics of reinforced concrete under mixed mode I-II load conditions are studied using three-point bending beams with a straight offset notch. Different offset ratios, different crack-depth ratios, and different sizes of reinforced concrete specimens and a set of concrete specimens as a control group were explored. The critical loads, the crack mouth opening displacements, the final failure angles, and the crack trajectory was recorded to analyze the fracture behavior of specimens under different factors. The 3D crack source locations by AE technique was adopted to locate the damage during the fracture process, which was in a good agreement with the crack propagation path obtained through the fracture test. A criterion, based on the simultaneous appearance of the rise of RA (rise time/peak amplitude), the decline of AF (counts/duration time), and Ib-value (ratio of weak events to strong events), was proposed to identify the three critical conditions in the mixed mode I-II fracture process, which include the initial crack at the notch tip, crack at the bottom of mid-span, and the peak load. Then, the fracture process was divided into four stages: initiation of micro-crack, stable crack propagation in a single path, stable crack propagation in double paths, and unstable crack propagation. The AE hits can accurately distinguish the moments of crack at mid-span and peak load. The modified AE parameters analysis method was utilized to classify the cracking mode at different stages of damage and the results showed that the shear cracks followed the tensile cracks, the proportion of AF to RA for common specimens in this study can be set to 80: 1, while that of small size specimen with a span length of 600 mm can be set to 40: 1. The results can provide a theoretical basis for the establishment of remote monitoring and early warning systems for large structures.

Effect of waste tyre rubber on mechanical and durability properties of concrete – A review

Abstract Disposal of waste tyre rubber has become a major environmental issue in all parts of the world representing a very serious threat to the ecology. One of the possible solutions for the use of scrap tyre rubber is to incorporate it into concrete, to replace some of the natural aggregate. An estimated 1000 million tyres reach the end of their useful lives every year and 5000 millions more are expected to be discarded in a regular basis by the year 2030. Up to now a small part is recycled and millions of tyres are just stockpiled, landfilled or buried. The volume of polymeric wastes like tyre rubber and polyethylene terephthalate bottles (PET) is increasing at a fast rate. This paper reviews the tests performed to determine the compressive strength, flexural tensile strength, water absorption and water penetration of using rubber tyre waste concrete samples. Scanning Electron Microscopy (SEM) images were also presented in this paper. It was observed that the compressive strength, flexural tensile strength and depth of water penetration of the rubberized concrete were less than that of the control mix, while the abrasion resistance and water absorption (up to 10% substitution) exhibited better results than that of the control mix concrete. This paper also reviews the performance of concrete mixtures incorporating 5%, 7.5% and 10% of discarded tyre rubber as aggregate and cement replacements. Numerous projects have been conducted on replacement of aggregates by crumb rubbers but scarce data are found on cementitious filler addition. Hence to examine characteristics of tyre crumb-containing concrete, two sets of concrete specimens were made. In the first set, different percentages by weight of chipped rubber were replaced for coarse aggregates and in the second set scrap-tyre powder was replaced for cement. Selected standard durability and mechanical test were performed and the results were analysed.

Evaluation of Three-Point Bending Fracture Tests of Selected Concrete: Crack Initiation and Acoustic Emission Parameters

In this paper, authors concentrate attention on crack initiation and acoustic emission (AE) parameters obtained from records of three-point bending fracture tests on eight sets of concrete specimens with initial stress concentrator at the age of 28 days. Resistance to stable and unstable crack propagation was quantified via evaluation of load vs crack mouth opening displacement diagrams using Double-K fracture model. The AE technique was used to monitor damage process taking place during testing in specimens.

Fresh State Properties of Concrete Incorporating Scrap Tire Rubber

The purpose of this work is to study fresh lightweight concrete containing recycled tire rubber aggregates. An experiment on concrete obtained by incorporating rubber aggregate with a ratio replacement of 5, 7.5 and 10% is done to evaluate the effect of these aggregates on the workability of two sets of concrete specimens. In the first set, coarse aggregates were replaced by different percentages by weight of granulate rubber and in the second set both coarse aggregates and sand were replaced rubber granulate and crumb rubber. Density, air content, compaction and slump tests are performed on the seven mixtures. Taking into account the density and water absorption differences between the natural aggregates and the rubber aggregates, the validity of the tests results are discussed. The results show that incorporating these rubber aggregates affects most rheological properties of lightweight concrete, for some application of concrete incorporating waste tire, rubber particles should be treated.

Strength and Durability Properties of Concrete with Starch Admixture

This paper examines some properties of concrete, such as strength, oxygen permeability and sorptivity using starch [cassava (CA) and maize (MS)] as admixtures. Concrete cubes containing different percentages of the CA and MS by weight of cement (0, 0.5, 1.0, 1.5 and 2.0 %) were cast. Compressive strength tests were carried out after 3, 7, 14, 21, 28, 56, 90, 180, 270 and 365 days of curing. Oxygen permeability and sorptivity tests were carried out on another set of concrete specimens with the same percentages of starch at 7, 28, 90, 180, 270 and 365 days. Oxygen permeability and sorptivity tests data obtained were subjected to Kruskal–Wallis one-way analysis of variance by ranks. The strength increase after 1 year over the control for CA 0.5 and CA 1.0 are 2.7 and 3.8 % respectively, while MS 0.5 and MS 1.0 gave 1.5 % increase over control. These results showed a decrease in oxygen permeability and rates of sorptivity, with concretes containing starch as admixtures giving better performance than the control concretes.

On the dispersion of data collected by in situ diagnostic of the existing concrete

The compressive strength of in-place concrete is a crucial mechanical parameter which influences the performance level and the safety assessment of existing RC structures both under seismic loads and under dead loads. Italian NTC and Eurocode 8 [1,2] have established that the fundamental basis of the safety assessment is the “Knowledge Level (KL)”, which shall be defined according to the procedures adopted for in situ inspection and materials testing (destructive and non-destructive). Within this framework – in the case of RC constructions – a major requirement is the explicit identification of the reference values for the strength of in situ concrete. The afore mentioned building codes, however, do not include any consideration about the uncertainty level affecting the results of in situ tests, which can indeed invalidate the reliability of the mechanical parameters. This problem is instead well addressed by FEMA 356 [3], which prescribes a limit value (14%) to the statistical dispersion of the measures performed on a set of concrete specimens. In this paper, after presenting and discussing a procedure applied for processing experimental data provided by in situ tests in a number of real case studies (school buildings in the Province of Foggia, Italy), the attention will be focused on the problem of the data scattering in the case of in situ concrete strength. It is shown that the variance is a crucial parameter, which should always be considered when performing the safety assessment, even if FEMA requirements, in this respect, are too much restrictive.

Scrap-tyre-rubber replacement for aggregate and filler in concrete

In this research the performance of concrete mixtures incorporating 5%, 7.5% and 10% of discarded tyre rubber as aggregate and cement replacements was investigated. Numerous projects have been conducted on replacement of aggregates by crumb rubbers but scarce data are found on cementitious filler addition in the literature. Hence to examine characteristics of tyre crumb-containing concrete, two sets of concrete specimens were made. In the first set, different percentages by weight of chipped rubber were replaced for coarse aggregates and in the second set scrap-tyre powder was replaced for cement. Selected standard durability and mechanical test were performed and the results were analysed. The mechanical tests included compressive strength, tensile strength, flexural strength and modulus of elasticity. The durability tests included permeability and water absorption. The results showed that with up to 5% replacement, in each set, no major changes on concrete characteristics would occur, however, with further increase in replacement ratios considerable changes were observed.

Using the Maturity Method in Concrete Produced with Setting Agents

The maturity function provides a reliable approach in the determination of the in situ strength of concrete at later ages. This study was aimed at determining the strength — maturity relationship on concrete specimens which were prepared using different admixtures and cured under different temperatures. For this reason, three sets of concrete specimens, having dimensions of 15×15×15 cm, were produced using the set accelerating admixture, set retarding admixture, and no admixture content at a constant consistency and 0.59 water-to-cement ratio. All hardened concrete specimens were cured at 0, 20, and 40°C temperatures under 100% humidity for 1, 3, 7, and 28 days. The compression tests were applied on specimens at the end of the curing time. Equations for the relationship between maturity and strength were worked out for the admixtures used in the study.

Effectiveness of concrete surface treatmentmaterials in reducing chloride-induced reinforcement corrosion

The effectiveness of concrete surface treatment materials, such as silane, siloxane, acrylic coating, etc., in reducing chloride-induced reinforcement corrosion was investigated. Two sets of reinforced concrete specimens were cast. In the first set, reinforcement corrosion was accelerated by impressing an anodic potential of 2 V and the time to cracking was monitored. The second set of concrete specimens were immersed in the chloride solution and reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. Among the surface treatment materials investigated, silane, silane/siloxane with top coat and acrylic coating were effective in reducing the rate of reinforcement corrosion. Furthermore, the data developed in this investigation indicated that the performance of coatings can be quickly evaluated using impressed current technique.

Effectiveness of concrete surface treatment materials in reducing chloride-induced reinforcement corrosion

The effectiveness of concrete surface treatment materials, such as silane, siloxane, acrylic coating, etc., in reducing chloride-induced reinforcement corrosion was investigated, Two sets of reinforced concrete specimens were cast. In the first set, reinforcement corrosion was accelerated by impressing an anodic potential of 2 V and the time to cracking was monitored. The second set of concrete specimens were immersed in the chloride solution and reinforcement corrosion was monitored by measuring corrosion potentials and corrosion current density. Among the surface treatment materials investigated, silane, silane/siloxane with top coat and acrylic coating were effective in reducing the rate of reinforcement corrosion. Furthermore, the data developed in this investigation indicated that the performance of coatings can be quickly evaluated using impressed current technique. (C) 1997 Elsevier Science Ltd.