Durability Performance Of Concrete Structures Research Articles

Performance of green high-strength concrete incorporating palm oil fuel ash in harsh environments

Abstract The corrosion of steel reinforcement by chloride is commonly recognized as a key factor that contributes to the degradation of durability in reinforced concreae structures. Using supplementary cementitious materials, such as industrial and agricultural waste materials, usually enhances the impermeability of the concrete and its corrosion resistance, acid resistance, and sulfate resistance. This study’s primary purpose is to examine the effects of replacing ordinary Portland cement (OPC) with ultrafine palm oil fuel ash (U-POFA) on the corrosion resistant performance of high-strength green concrete (HSGC). There were four HSGC mixes tested; the first mix contained 100% OPC, while the other mixes replaced OPC mass with 20%, 40%, and 60% of U-POFA. The performance of all HSGC mixes containing U-POFA on workability, compressive strength, porosity, water absorption, impressed voltage test, and mass loss was investigated at 7, 28, 60, and 90 days. Adding U-POFA to mixes enhances their workability, compressive strength (CS), water absorption, and porosity in comparison with mixes that contain 100% OPC. The findings clearly portrayed that the utilization of U-POFA as a partial alternative for OPC significantly enhances the corrosion-resistant performance of the HSGC. In general, it is strongly advised that a high proportion of U-POFA be incorporated, totaling 60% of the OPC content. This recommendation is the result of its significance as an environmentally friendly and cost-effective green pozzolanic material. Hence, it could contribute to the superior durability performance of concrete structures, particularly in aggressive environmental exposures. Highlights The corrosion resistance performance of high-strength green concrete was investigated. Ultrafine palm oil fuel ash as a partial alternative of cement mass with 20%, 40%, and 60% was used. HSGC performance was evaluated in terms of workability, compressive strength, water absorption, porosity, impact stress testing, and mass loss.

Assessment of Durability Indicators for Service Life Prediction of Portland Limestone Cementitious Systems Produced with Permeability-Reducing Admixtures

Supplementary cementing materials (SCMs) and the challenges associated with admixture compatibility and durability performance are continuous challenges for the construction industry. Utilizing SCMs has apparent benefits in reducing the carbon footprint and improving the durability performance of concrete structures. This work investigates the performance of mortars composed of Portland limestone cement, calcium carbonate, butyl stearate, and oleic acid. The effort focuses on transport properties using electrical resistivity, chloride migration, porosity, and water permeability measurements. Then, various methods based on the last parameters are compared to assess the changes in the effective chloride diffusion coefficient and the intrinsic liquid water permeability. Measurements for drying shrinkage, thermal expansion, and compressive strength are conducted to verify durability and mechanical performance. The effect of the admixture addition on the service life of a structure fully submerged in marine exposure conditions is then evaluated using Fick’s second law of diffusion and the approach described by FIB model code 34. The results indicate that incorporating calcium carbonate, butyl stearate, and oleic acid in mortar mixtures provides enhanced durability compared to plain Portland limestone cement mortars.

Effects of pure carbonation on pore structure and water permeability of white cement mortars

The effects of carbonation on cement-based materials have drawn much attention because of its profound influences on durability performance of concrete structures. Most accelerated carbonation in lab is conducted at RH 50%–70%, which also dries out cement-based materials. The introduced drying action changes pore structure significantly, making the effects of carbonation obscure. To clarify the effects of pure carbonation, water permeability and related micro-structural characteristics are measured on mature mortars, which have been carbonated at water-saturated state. It is found that after carbonation, the porosity of mortars decreases slightly, with finer overall pore structure and lower characteristic pore size. The water permeability also decreases by roughly 40% on average. Based on the pore size distribution curves obtained through the low-field proton nuclear magnetic resonance technique, water permeability is predicted by the Katz-Thompson and Kozeny-Carman theories with satisfactory accuracy. The decrease of water permeability after carbonation agrees well with the reduced characteristic pore length, which quantitatively verifies the observed refinement of nanoscale pore structure due to pure carbonation.

Analytical models to estimate efficiency of capsule-based self-healing cementitious materials considering effect of capsule shell thickness

Capsule-based self-healing materials are a promising solution for maintaining the mechanical properties and durability performance of concrete structures. To assess the efficiency of capsule-based self-healing cementitious material, analytical models considering the effect of the capsule shell thickness were derived for three common capsule shapes: sphere (SPH), cylinder (CYL), and a cylinder with spherical tips (CST). A numerical simulation method was used to validate the proposed analytical models. A parametric study was conducted to investigate the effect of the capsule diameter, aspect ratio, and shell thickness on the self-healing efficiency. Simplified analytical models were derived to calculate the capsule diameter, aspect ratio, and shell thickness for the shape design and manufacturing of the capsule. The results of this study show that: (1) the self-healing efficiency is proportional to the diameter of the capsule; (2) the self-healing efficiency increases approximately linearly with an increase in the aspect ratio for CYL and CST capsules; (3) the self-healing efficiency may be greatly over-estimated without considering the shell thickness, especially for spherical capsules.

Impact of CO2 curing on the microhardness and strength of 0.35 w/c cement paste: Comparative study of internal/surface layers

The aim of this paper is to investigate the effect of carbonation on the microhardness and mechanical-related properties of carbonated and uncarbonated layers of cement pastes. The microhardness and mechanical property changes were examined 1 day after demolding and then 3, 7, 14, and 28 days with further CO2 and water curing. CO2 treatment yielded substantial impacts on the microstructure and densification of the surface layer of the paste by consuming calcium hydroxide and forming calcium carbonates. The maximum carbonation depth of 5 mm was recorded at 28 days, and the microhardness of the surface layer was significantly enhanced compared to the internal layer as well as uncarbonated paste samples. However, despite improved surface hardness, the overall compressive strength of carbonated sample was lower than that of water-cured samples, probably due to the non-preconditioning (to remove excess water for carbonation) of the carbonated samples and better hydration in the internal layer of the samples cured in water. In addition, the thin denser surface layer of the carbonated samples could decrease the cement hydration process. However, the denser and lower surface water absorption relation to CO2 treatment could facilitate long-term durability performance of concrete structures.

Coupled application of innovative electromagnetic sensors and digital image correlation technique to monitor corrosion process of reinforced bars in concrete

Corrosion monitoring of reinforcement is of great importance in evaluating the durability performance of concrete structures, especially under harsh environments. This paper presents a creative approach that combine using innovative electromagnetic monitoring apparatus (EMMA) and digital image correlation (DIC) technique in order to monitor the reinforcement corrosion inside concrete. The new-type electromagnetic sensor is capable of evaluating the corrosion degree of reinforced bars in concrete, meanwhile, DIC technique is always used to detect the tiny corrosion-triggered deformation on concrete surface. The result shows that joint use of these two techniques can monitor the entire process from corrosion initiation to further corrosion-induced strain variation on the surface of concrete. Besides, concrete beam with higher vertical load level leads to greater bending movement, which will accelerate the corrosion behavior and limit the horizontal strain. Moreover, the characteristics of DIC technique and strain gauges are compared respectively.

Determining the service life extension of silane treated concrete structures: A probabilistic approach

Silane impregnation is a widely used surface protection method in practical engineering for enhancing the durability performance of concrete structures in chloride rich environments. Here a probabilistic model, together with the statistical properties of model parameters, is proposed, to determine the service life extension effect contributed by the silane impregnation considering various uncertainties. The corrosion free service life of silane-impregnated concrete structures is predicted based on the well-developed reliability theory. The model is solved in a numerical way in which Latin hypercube sampling is used to balance the efficiency and precision of the uncertainty analysis. The model is validated through comparisons with on-site exposure data. Through the analysis the importance of considering uncertainties is confirmed which may significantly influence the protective effect of silane impregnation. Further analyses reveal that the service life extension effect of silane may be shorter than the assumptions in many existing studies and an earlier application is more beneficial.

Corrosion Prediction with Parallel Finite Element Modeling for Coupled Hygro-Chemo Transport into Concrete under Chloride-Rich Environment

The prediction of the chloride-induced corrosion is very important because of the durable life of concrete structure. To simulate more realistic durability performance of concrete structures, complex scientific methods and more accurate material models are needed. In order to predict the robust results of corrosion initiation time and to describe the thin layer from concrete surface to reinforcement, a large number of fine meshes are also used. The purpose of this study is to suggest more realistic physical model regarding coupled hygro-chemo transport and to implement the model with parallel finite element algorithm. Furthermore, microclimate model with environmental humidity and seasonal temperature is adopted. As a result, the prediction model of chloride diffusion under unsaturated condition was developed with parallel algorithms and was applied to the existing bridge to validate the model with multi-boundary condition. As the number of processors increased, the computational time decreased until the number of processors became optimized. Then, the computational time increased because the communication time between the processors increased. The framework of present model can be extended to simulate the multi-species de-icing salts ingress into non-saturated concrete structures in future work.

Durability Performance of Concrete Structures Built with Low Carbon Construction Materials

Here, we demonstrate the feasibility of industrial application of low carbon supplementary cementitious materials (i.e. geopolymer concrete) by investigating the durability performance of eight years aged reinforced geopolymer concrete structure exposed to ambient environment. The corrosion performance of reinforcement bar in concrete and permeability characteristic of cover concrete is investigated by using non-destructive techniques. The results reveal that the reinforcement in geopolymer concrete exhibits higher corrosion risk in atmospheric environment and this attributes to the deterioration of long term durability performance for geopolymer concrete.

Chloride Ion Penetrability of HPFRCC after Loading

Cracking is one of the most important factors in the serviceability as well as durability performance of concrete structures. Recently, it was recognized that a high performance fiber-reinforced cementitious composite (HPFRCC) provides a possible solution to this inherent problem of cracking by smearing one or several dominant cracks into many distributed microcracks. The purpose of the present study is to explore the ductility characteristics of HPFRCC. The permeability of HPFRCC after subjected to different load levels were measured to identify the effect of reduced cracking among the mixtures. It was confined that the permeability of proposed mixtures was lower than that without microfibers. This means that the proposed materials can reduce the crack width greatly at the same applied loads

Volume and deviator creep of calcium-leached cement-based materials

This paper provides new experimental evidence of the specific volume creep and deviator creep of cement-based materials. Creep tests conducted on calcium-leached cement pastes and mortars under various triaxial loading conditions provide conclusive evidence of a specific short-term creep and a specific long-term creep. It is found that at least two competing dissipative mechanisms are at work in short-term creep of cement-based materials: (1) a creep relaxation mechanism in the calcium–silicate–hydrate (C–S–H) solid phase activated by microstress concentrations in the heterogeneous microstructure; and (2) stress relaxation by microcracking beyond a relatively small stress threshold. If the first dominates over the second, the short-term volume creep is contracting, and in the inverse case, a short-term dilating behavior is found. Furthermore, provided that microcracking stabilizes during the short-term creep, the long-term creep occurs at constant volume. Based on these results, we argue that the concept of a creep Poisson's ratio, which is commonly employed in engineering practice to extrapolate uniaxial creep tests to multiaxial stress conditions, should be abandoned when triaxial stress states affect the durability performance of concrete structures.