C.C. Yang

Approximate migration coefficient of interfacial transition zone and the effect of aggregate content on the migration coefficient of mortar

Abstract In this study, the electrochemical technique is applied to accelerate chloride ion migration in mortar to estimate its transport properties. In order to investigate the effect of aggregate content on the chloride migration coefficient of mortar, specimens with different fine aggregate volume fractions were cast and tested. The chloride migration coefficient of mortar was determined experimentally as a function of the volume fraction of aggregate. The chloride migration coefficient of mortar is used to assess the dilution, tortuosity and interfacial transition zone (ITZ) effects of aggregate in the cement-based composites. A model modified from the Bruggeman theory for the migration coefficient of mortar is used, and the regression analysis is used to determine the approximate chloride migration coefficient of ITZ. Based on the experimental and regression analytical results, the approximate ITZ migration coefficient is 2.83, 1.76 and 1.55 times of the matrix migration coefficient for the ITZ with the thickness of 20, 40 and 50 μm, respectively.

Effect of aggregate properties on the strength and stiffness of lightweight concrete

Abstract An experimental program was carried out to obtain the compressive strengths and elastic moduli of cold-bonded pelletized lightweight aggregate concretes. Three types of aggregates were made with different fly ash contents. Experimental data were analyzed statistically. Test results of multivariate analysis of variance (MANOVA) with 95% confidence level ( α =0.05) show that the properties of lightweight aggregates and the water/binder ratio are two significant factors affecting the compressive strength and elastic modulus of concrete.

Effect of the Transition Zone on the Elastic Moduli of Mortar

Abstract In order to investigate the behavior of transition zone and the effect of transition zone on the elastic modulus of mortar, cubic specimens (50 × 50 × 50 mm) with different volume fractions (volume of aggregate/volume of mortar, a/t = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) of aggregate were cast and tested. The Double-Inclusion method and Mori-Tanaka theory were used to predict the elastic moduli of three-phase (aggregate, transition zone, and cement paste) composite materials. A comparison was also made between the theoretical results and experimental data. Based on this comparison, when the thickness of transition zone is 20 μm, the average Young’s modulus of transition zone is about 20 to 40% of the matrix modulus. When the thickness of transition zone is 40 μm, the average Young’s modulus of transition zone is about 50 to 70% of the matrix modulus. Test results show that the overall elastic properties of the composite depend mainly on the volume fraction of aggregate.

A two-phase model for predicting the compressive strength of concrete

In order to study the strength of concrete, cement-based composite material specimens with different volume fractions (10%, 20%, and 30%) of aggregate and two water/(cement + silicafume) ratios (wb = 0.28 and 0.6) were cast and tested. Theoretical analysis was investigated in this study by employing the theory of micromechanics. A new approach is proposed to obtain the average stress fields of inhomogeneities and matrix by use of the equivalent inclusion method and the concept of Mori-Tanaka theory. The uniaxial compressive strength of cement-based composite materials can be considered as a function of component properties of composite, and the volume fraction of aggregate. The compressive strength of concrete is controlled by the weakest component. The comparison is also made between theoretical results and the experimental data.

The relationship between charge passed and the chloride-ion concentration in concrete using steady-state chloride migration test

The accelerated chloride migration test in this study is a modified version of the ASTM C1202-97 or AASHTO T277-96 (RCPT) method. The current, chloride-ion concentration and temperature were measured during the experiment. Four different concretes used for test had a water to cementitious ratio of 0.4, containing various mineral admixtures. The transport properties were investigated using the accelerated chloride migration test. At a steady-state chloride flux, a good correlation was found between the charge passed (obtained by integrating the current-time curve) and the chloride-ion concentration.

Double inclusion model for approximate elastic moduli of concrete material

Abstract The overall elastic moduli of concrete composite materials are investigated in this study by employing the theory of micromechanics. A method based on Mori-Tanaka Theory and double inclusion can provide a more accurate evaluation of the average elastic relationships of concrete composite materials. The inclusions are divided into two groups: fine aggregate and coarse aggregate. Moreover, the overall elastic moduli of the concrete composite materials are given as a function of properties and volume fraction of the following three components: fine aggregate, coarse aggregate, and cement paste. A comparison is also made between the theoretical results and published experimental data.

Condition assessment of reinforced concrete beams relative to reinforcement corrosion

Abstract The main aim of this paper is to evaluate the corrosion condition of reinforced concrete (RC) beams and to assess the structural behavior of corroded reinforced concrete beams. Thirty two beams were tested, of which 16 had predetermined cracks. An impressed current was applied to the beams in order to accelerate steel corrosion. Electrochemical measurements were carried out to obtain open circuit potentials and corrosion rates of the embedded steels and loading tests were conducted on the beams to measure the ultimate moment. Test results show that there existed a fair relationship between the loading capacity reduction and the corrosion condition of the RC beams.

Approximate elastic moduli of lightweight aggregate

This study presents a method for the estimation of the elastic modulus of lightweight aggregate. In order to investigate the elastic modulus of aggregate and the effect of aggregate content on the elastic modulus of lightweight concrete, cylindrical specimens with different volume ratios (volume ratio of coarse aggregate/total aggregate) and various water/cement ratios were cast and tested. Both single inclusion and double inclusion models were applied to predict the elastic moduli of two-phase and three-phase cement-based composite materials, respectively. The elastic moduli of sand and coarse aggregate were derived from the experimental results using the theoretical models.

A pullout test for determining interface properties between rebar and concrete

In this study, the rebar-concrete interface properties were investigated by conducting the single rebar pullout test. Using a combination of the stress approach and fracture mechanical theory, the corresponding material parameters were obtained and the model was verified as being suitable for reinforced concrete composite material. Advanced Cement Based Materials 1997, 5, 57–65.