Effect of Delay in Testing Asphalt Concrete Specimens for Marshall Stability, MLR-86-08, Draft, 1986

The Central Laboratory has been delaying the mix design testing of 2 1/2" X 4" Marshall specimens for stability, until the next day after molding. For example, if the mixes are made and samples molded on Friday a man would have to come in and work on Saturday to test these specimens. The reason for this is that the ASTM-01559 "Resistance to Plastic Flow of Bituminous Mixes Using Marshall Apparatus," states that "the specimens after being molded shall be carefully transferred to a smooth, flat surface and allowed to stand overnight at room temperature, before being weighed, measured and tested." The AASHTO procedure, AASHTO Designation T-245-82 "Resistance to Plastic Flow of Bituminous Mixtures using Marshall Apparatus," does not say when the specimens shall be tested for stability. The IDOT Lab. Specifications, Test Method No. Iowa 502-8 and test method No. Iowa 506-C "compacting asphaltic concrete by the Marshall Method" and "Resistance to Plastic Flow of Bituminous Mixtures Using the Marshall Apparatus," respectively, only state that the specimens shall be cooled before testing. Due to the above conflict in specifications, a number of mix samples were tested, in the Central Lab, for stability on different days. This should furnish enough information to allow us to change the procedure and to test for stability the same day molded, or be able to delay the testing for 3 days or more.

Image Analysis for Evaluating Air Void Parameters of Concrete, HR-396, 1998

This research project investigated the use of image analysis to measure the air void parameters of concrete specimens produced under standard laboratory conditions. The results obtained from the image analysis technique were compared to results obtained from plastic air content tests, Danish air meter tests (also referred to as Air Void Analyzer tests), high-pressure air content tests on hardened concrete, and linear traverse tests (as per ASTM C-457). Hardened concrete specimens were sent to three different laboratories for the linear traverse tests. The samples that were circulated to the three labs consisted of specimens that needed different levels of surface preparation. The first set consisted of approximately 18 specimens that had been sectioned from a 4 in. by 4 in. by 18 in. (10 cm by 10 cm by 46 cm) beam using a saw equipped with a diamond blade. These specimens were subjected to the normal sample preparation techniques that were commonly employed by the three different labs (each lab practiced slightly different specimen preparation techniques). The second set of samples consisted of eight specimens that had been ground and polished at a single laboratory. The companion labs were only supposed to retouch the sample surfaces if they exhibited major flaws. In general, the study indicated that the image analysis test results for entrained air content exhibited good to strong correlation to the average values determined via the linear traverse technique. Specimens ground and polished in a single laboratory and then circulated to the other participating laboratories for the air content determinations exhibited the strongest correlation between the image analysis and linear traverse techniques (coefficient of determination, r-squared = 0.96, for n=8). Specimens ground and polished at each of the individual laboratories exhibited considerably more scatter (coefficient of determination, r-squared = 0.78, for n=16). The image analysis technique tended to produce low estimates of the specific surface of the voids when compared to the results from the linear traverse method. This caused the image analysis spacing factor calculations to produce larger values than those obtained from the linear traverse tests. The image analysis spacing factors were still successful at distinguishing between the frost-prone test specimens and the other (more durable) test specimens that were studied in this research project.

Development of In Situ Detection Methods for Materials-Related Distress (MRD) in Concrete Pavements: Phase 2, HR-1081, 2005

This project utilized information from ground penetrating radar (GPR) and visual inspection via the pavement profile scanner (PPS) in proof-of-concept trials. GPR tests were carried out on a variety of portland cement concrete pavements and laboratory concrete specimens. Results indicated that the higher frequency GPR antennas were capable of detecting subsurface distress in two of the three pavement sites investigated. However, the GPR systems failed to detect distress in one pavement site that exhibited extensive cracking. Laboratory experiments indicated that moisture conditions in the cracked pavement probably explain the failure. Accurate surveys need to account for moisture in the pavement slab. Importantly, however, once the pavement site exhibits severe surface cracking, there is little need for GPR, which is primarily used to detect distress that is not observed visually. Two visual inspections were also conducted for this study by personnel from Mandli Communications, Inc., and the Iowa Department of Transportation (DOT). The surveys were conducted using an Iowa DOT video log van that Mandli had fitted with additional equipment. The first survey was an extended demonstration of the PPS system. The second survey utilized the PPS with a downward imaging system that provided high-resolution pavement images. Experimental difficulties occurred during both studies; however, enough information was extracted to consider both surveys successful in identifying pavement surface distress. The results obtained from both GPR testing and visual inspections were helpful in identifying sites that exhibited materials-related distress, and both were considered to have passed the proof-of-concept trials. However, neither method can currently diagnose materials-related distress. Both techniques only detected the symptoms of materials-related distress; the actual diagnosis still relied on coring and subsequent petrographic examination. Both technologies are currently in rapid development, and the limitations may be overcome as the technologies advance and mature.

Identification of steel bars immersed in reinforced concrete based on experimental results of eddy current testing and artificial neural network analysis

This paper presents an experimental research on the use of eddy current testing (ECT) and artificial neural networks (ANNs) in order to identify the gauge and position of steel bars immersed in concrete structures. The paper presents details of the ECT probe and concrete specimens constructed for the tests, and a study about the influence of the concrete on the values of measured voltages. After this, new measurements were done with a greater number of specimens, simulating a field condition and the results were used to generate training and validation vectors for multilayer perceptron ANNs. The results show a high percentage of correct identification with respect to both, the gauge of the bar and of the thickness of the concrete cover. © 2013 Copyright Taylor and Francis Group, LLC.

Influence of time evolution in the modulus of elasticity of concrete reinforced by carbon fibers

The modulus of elasticity is an important property for the behavior analysis of concrete structures. This research evaluated the strain difference between concrete specimens with and without the application of laminate carbon fiber composites as well as the variation time, in months, of the axial strength compression and modulus of elasticity. Through the experimental results, it is concluded that increases in compressive strength and modulus of elasticity are more significant in the specimens without reinforcement.

A study of acoustic emission technique for concrete damage detection

The Acoustic emission (AE) technique, as one of non-intrusive and nondestructive evaluation techniques, acquires and analyzes the signals emitting from deformation or fracture of materials/structures under service loading. The AE technique has been successfully applied in damage detection in various materials such as metal, alloy, concrete, polymers and other composite materials. In this study, the AE technique was used for detecting crack behavior within concrete specimens under mechanical and environmental frost loadings. The instrumentations of the AE system used in this study include a low-frequency AE sensor, a computer-based data acquisition device and a preamplifier linking the AE sensor and the data acquisition device. The AE system purchased from Mistras Group was used in this study. The AE technique was applied to detect damage with the following laboratory tests: the pencil lead test, the mechanical three-point single-edge notched beam bending (SEB) test, and the freeze-thaw damage test. Firstly, the pencil lead test was conducted to verify the attenuation phenomenon of AE signals through concrete materials. The value of attenuation was also quantified. Also, the obtained signals indicated that this AE system was properly setup to detect damage in concrete. Secondly, the SEB test with lab-prepared concrete beam was conducted by employing Mechanical Testing System (MTS) and AE system. The cumulative AE events and the measured loading curves, which both used the crack-tip open displacement (CTOD) as the horizontal coordinate, were plotted. It was found that the detected AE events were qualitatively correlated with the global force-displacement behavior of the specimen. The Weibull distribution was vii proposed to quantitatively describe the rupture probability density function. The linear regression analysis was conducted to calibrate the Weibull distribution parameters with detected AE signals and to predict the rupture probability as a function of CTOD for the specimen. Finally, the controlled concrete freeze-thaw cyclic tests were designed and the AE technique was planned to investigate the internal frost damage process of concrete specimens.

Effect of the curing conditions of concrete on the behaviour under freeze-thaw cycles*

The aim of this work is to relate the curing conditions of concrete and the addition of an air-entraining admixture with the damage caused by freeze–thaw cycles. In countries with a continental climate, the curing of concrete in summer is performed under climatic conditions of high temperature and low humidity, and during the winter the concrete suffers conditions of freeze–thaw, often accompanied by the use of de-icing salts. This paper shows the experimental results of the behaviour of concrete specimens cured under climatic summer conditions (high temperature and low humidity) and then subjected to freeze–thaw cycles. Curing of the specimens includes conditions of good and bad practice in relation to wetting and protection of the concrete. It also examines the effectiveness of using an air-entraining admixture in both cases. The experimental programme includes an evaluation of the mechanical properties of the concrete, the study of the cement hydration and the measurement of the volume and pore sizes of the concrete. These tests were performed before and after the application of the freeze–thaw cycles. The results obtained showed that the specimens without air-entraining admixture show a deterioration of mechanical properties after the freeze–thaw test. However, the inclusion of air bubbles benefits the behaviour of concrete against freeze–thaw cycles so even better mechanical properties after the test were observed. This anomalous behaviour is because the cement hydration process continues over the freeze–thaw tests, closing the pore structure. This aspect has been confirmed with the DTA and TG tests performed

Study of the damage evolution of the concrete under freeze-thaw cycles using traditional and non-traditional techniques

Some experiments have been performed to investigate the cyclic freeze-thaw deterioration of concrete, using traditional and non-traditional techniques. Two concrete mixes, with different pore structure, were tested in order to compare the behavior of a freeze-thaw resistant concrete from one that is not. One of the concretes was air entrained, high content of cement and low w/c ratio, and the other one was a lower cement content and higher w/c ratio, without air-entraining agent. Concrete specimens were studied under cyclic freeze-thaw conditions according to UNE-CENT/TS 12390-9 test, using 3% NaCl solution as freezing medium (CDF test: Capillary Suction, De-icing agent and Freeze-thaw Test). The temperature and relative humidity were measured during the cycles inside the specimens using embedded sensors placed at different heights from the surface in contact with the de-icing agent solution. Strain gauges were used to measure the strain variations at the surface of the specimens. Also, measurements of ultrasonic pulse velocity through the concrete specimens were taken before, during, and after the freeze-thaw cycles. According to the CDF test, the failure of the non-air-entraining agent concrete was observed before 28 freeze-thaw cycles; contrariwise, the scaling of the air-entraining agent concrete was only 0.10 kg/m 2 after 28 cycles, versus 3.23 kg/m 2 in the deteriorated concrete, after 28 cycles. Similar behavior was observed on the strain measurements. The residual strain in the deteriorated concrete after 28 cycles was 1150 m versus 65 m, in the air-entraining agent concrete. By means of monitoring the changes of ultrasonic pulse velocity during the freeze-thaw cycles, the deterioration of the tested specimens were assessed

Evaluation offreeze-thaw damage in concrete by ultrasonic imaging

This work studies the use of ultrasonic imaging as an evaluation tool in concrete subjected to freeze–thaw (F–T) cycles. To evaluate the damage in this deterioration process, ultrasonic velocity and attenuation images have been generated from concrete specimens with and without air-entraining agents. Two parameters have been proposed from these ultrasonic images according to our experimental setup: the non-assessable area proportion (NAAP) and a weighted average velocity in terms of the NAAP. The proposed parameters have been compared with the recommended failure criteria of the ASTM and Rilem standards, which employ ultrasonic contact measurements. The principal advantage of the use of ultrasonic images and the proposed methodology in comparison with the ultrasonic velocity measurements by contact is the possibility of detection of incipient damage caused by accelerated freeze–thaw cycles.

Experimental and numerical analysis of concrete Slabs subjected to Blast

This paper summarizes the research activities focused on the behaviour of concrete and concrete structures subjected to blast loading carried out by the Department of Materials Science of the Technical University of Madrid (PUM). These activities comprise the design and construction of a test bench that allows for testing up to four planar concrete specimens with one single explosion, the study of the performance of different protection concepts for concrete structures and, finally, the development of a numerical model for the simulation of concrete structural elements subjected to blast. Up to date 6 different types of concrete have been studied, from plain normal strength concrete, to high strength concrete, including also fibre reinforced concretes with different types of fibres. The numerical model is based on the Cohesive Crack Model approach, and has been developed for the LSDYNA finite element code through a user programmed subroutine. Despite its simplicity, the model is able to predict the failure patterns of the concrete slabs tested with a high level of accuracy

Radiological impact of cement, concrete and admixtures in Spain

It has been analyzed samples of portland cement (PC) with and without admixtures, samples of calcium aluminate cement (CAC) with different content of Al2O3 and specimens of concrete made with PC and CAC using High Resolution Gamma Spectrometry. The activity concentration index (I) is much less than 0.5 mSv y-1 for all the concrete specimens according to the Radiation protection document 112 of the European Commission. The PC without admixtures (CEM I 52,5 R) and the PC with addition of limestone (CEM II/BL 32,5 N) also have an I value much lower than 0.5 and the PC with the addition of fly ash and blast furnace slag (CEM IV/B (V) 32,5 N and III/A 42.5 N/SR) have an I value close to 0.6. The I value of the CAC used in the manufacture of structural precast concrete is of the order of 1 mSv y-1. Some of the CAC used in refractory concrete reaches a value close to 2 mSv y-1.

An improved procedure for obtaining and maintaining well characterized partial water saturation states on concrete samples to be used for mass transport tests

A conditioning procedure is proposed allowing to install into the concrete specimens any selected value of water saturation degree with homogeneous moisture distribution. This is achieved within the least time and the minimum alteration of the concrete specimens. The protocol has the following steps: obtaining basic drying data at 50 °C (water absorption capacity and drying curves); unidirectional drying of the specimens at 50 °C until reaching the target saturation degree values; redistribution phase in closed containers at 50 °C (with measurement of the quasi-equilibrium relative humidities); storage into controlled environment chambers until and during mass transport tests, if necessary. A water transport model is used to derive transport parameters of the tested materials from the drying data, i.e., relative permeabilities and apparent water diffusion coefficients. The model also allows calculating moisture profiles during isothermal drying and redistribution phases, thus allowing optimization of the redistribution times for obtaining homogeneous moisture distributions.

Recommendation of RILEM TC 178-TMC: Testing and modelling chloride penetration in concrete

This RILEM Technical Recommendation intends to give a general description of methods of sampling for obtaining chloride concentration profiles in concrete, applicable both for laboratory cast concrete specimens, for concrete cores taken from structures and for testing on site. These sampling procedures may be applied for obtaining concentration profiles of any other chemical species present in concrete.

Microstructural analysis of surface and interface zones in concrete

Several of OPC paste and concrete specimens, with different mix proportions, were cast against CPF and impermeable formwork (IF) and the profiles of pore structure, microhardness and scratch hardness of the cover zone were established. The chloride ingress and the depth of carbonation of the surface zone of concrete cast against CPF and IF were investigated. The main mechanisms controlling the ECR processes and the factors affecting such treatment were critically reviewed. Subsequently, as a means of restoring passivation of steel embedded in carbonated concrete, such HCP specimens were subjected to ECR. The influence of ECR on the chemistry of the pore solution and the microstructure of the surface and the steel/cement past interface zones were also studied. The main findings of this investigation were as follows: (a) The thickness of the microstructure gradient of cover concrete is significantly decreased with increasing period of water curing but is relatively unaffected by curing temperature, w/e ratio and the use of cement replacement materials. (b) The scratch hardness technique was shown to be potentially useful for characterising the microstructure and microhardness gradients of the surface zone. (c) A relationship between the microstructure gradient and mass transport properties of the surface zone was established. (d) The use of CPF resulted in a significant reduction in porosity of both the cement paste matrix and the aggregate/cement paste transition zone, and a marked improvement in the resistance of the surface zone to carbonation and the ingress of chloride ions. (e) The ECR treatment resulted in a marked densification of the pore structure and in changes to the pore solution chemistry and the cement phases of near-surface and steel/cement paste transition zones. This effect was more pronounced with current density, period of treatment and particularly with the use of sodium phosphate as an electrolyte.

Chloride resistance and durability of cement paste and concrete containing metakaolin

Metakaolin (MK), a calcined clay, was included as a partial cement replacement material, at up to 20% by weight of binder, in cement pastes and concrete, and its influence on the resistance to chloride ingress investigated. Reductions in effective chloride diffusion coefficients through hardened cement paste were obtained for binary blends and by combining OPC, MK and a second cement replacement material of pulverised fuel ash or ground granulated blast furnace slag. Steady state oxygen diffusion measurements through hardened cement pastes measured using an electrochemical cell showed that the interaction between charged species and the pore surfaces is a major factor in determining chloride diffusion rate. Rheology of the binder, particularly at high MK replacement levels, was found to have a dramatic influence on the diffusion performance of cement pastes. It was concluded that plasticising admixtures are essential for adequate dispersion of MK in cement pastes. Chloride concentration profile analysis of the concrete cylinders, exposed to sodium chloride solution for one year, was employed to obtain apparent chloride diffusion coefficients for concrete specimens. MK was found to reduce the depth of chloride penetration into concrete when compared with that of unblended mixes. Corrosion rate and corrosion potential measurements were taken on steel bars embedded in concrete exposed to a saline environment under conditions of cyclic wetting and drying. The initiation time for corrosion was found to be significantly longer for MK blended mixes than for plain OPC systems. The aggregate-paste interfacial zone of MK blended systems was investigated by steady state diffusion of chloride ions through mortar containing glass beads as model aggregate. For the model aggregate specimens tested the work confirmed the hypothesis that properties of the bulk paste are the controlling factors in ionic diffusion through mortar.