Carbonation Of Concrete Structures Research Articles

A framework for predicting the carbonation depth of concrete incorporating fly ash based on a least squares support vector machine and metaheuristic algorithms

The carbonation of concrete structures is becoming a more serious problem as the global CO2 level increases, and poses a great challenge to concrete durability research. In this study, a hybrid prediction framework on the basis of the least squares support vector machine (LSSVM) and metaheuristic algorithms is proposed to accurately predict the carbonation depth of concrete incorporating fly ash. The fly ash replacement level, cement content, water-to-binder ratio, CO2 content, relative humidity of environmental and exposure time are treated as input variables of the framework. A database containing 500 sets of samples is created for model building and comparison. The results show that five hybrid models have superior accuracy in the prediction of concrete carbonation depth, where the R2, RMSE, MAE and VAF range from 0.9683 to 0.9819, 1.7309–2.2936 mm, 1.2255–1.5478 mm, and 96.8317 to 98.1995, respectively. In addition, the proposed prediction framework has better performance (i.e., smaller RMSE) compared to reported empirical prediction models. The Sobol' global sensitivity index analysis results indicate that the water-to-binder ratio, exposure time and cement content have higher sensitivity to predict the carbonation depth. The effect of dataset division ratio on the models (an aspect that has not been investigated in previous research) is further explored in this study, and the optimal dataset division ratio for each model is determined.

Diagnosing and repairing carbonation in concrete structures

This paper concentrates on the carbonation of concrete, but also provides a brief synopsis of varying defects in concrete when used as a building material. It outlines the different defects that can arise with concrete, discusses the cause of these defects, and puts forward industry-recommended remedial action. It also uses live case study examples of the solutions to prolonging the life expectancy of external concrete facades.

Factors Affecting Carbonation of Railway Rigid-Frame Viaducts

Recent years have seen a considerable amount of research on the carbonation of concrete. The standard specifications for concrete structures, outlined by the Japan Society of Civil Engineers (JSCE), prescribe a method to verify the durability of concrete structures in relation to carbonation. However, as the carbonation rate is largely governed by environmental conditions, it is important to quantitatively assess the effect of these conditions on the carbonation of concrete structures by applying the method to actual structures.The factors affecting the progress of carbonation in different members were investigated based on the results of a survey on a rigid-frame railway viaduct in service since its construction several decades before. The study results indicate that the carbonation rate of columns varies with height and depends on the exposure condition to rainwater. In contrast, the dis-persion of the carbonation depth on beams and slabs is small when compared to that of the carbonation depth on columns.

공극률을 고려한 콘크리트 중의 이산화탄소 확산특성에 관한 연구

초록·키워드 목차 오류제보하기 등록된 정보가 없습니다. ABSTRACT1. 서론2. 콘크리트의 공극률 계산과정3. 실험개요4. 실험결과 및 고찰5. 이산화탄소 확산계수 실험식6. 결론참고문헌요약

A study on carbonation in concrete structures at existing cracks

The carbonation depth of concrete is an important index for evaluating the damage and durability of reinforced concrete structures. In this paper, the main purpose focuses on the study of carbonation problems of concrete structures at existing cracks. The carbonation process of concrete structures at cracks consists of four steps: diffusion of CO2 into the crack, diffusion of CO2 into the concrete, chemical reaction, and diffusion of hydroxyl ions. The present study indicates that the coefficient of carbonation rates of both uncracked and cracked concrete structures follow normal distribution. As regards the pure process of carbonation, the same basic interrelations given for uncracked concrete are valid for carbonation in the crack regions as well. Carbonation can penetrate into the interior of cracked concrete much faster than it does through uncracked concrete. Under static loading of existing reinforced concrete structures with cracks, the carbonation depth at a constant crack width can be predicted by using statistical methods.

Carbonation of concrete structures in hot dry coastal regions

This paper reports the results of a condition survey of 50 concrete buildings undertaken in the State of Kuwait. Concrete cores were extracted from walls and columns of these buildings and their density, compressive strength and depth of carbonation were evaluated. The buildings surveyed in the hot dry salty environment carbonated, on average, a little more than 1 mm per year. The coastal buildings, however, carbonated at a higher rate than the near-coastal and inland buildings. The results of this survey have furnished realistic values of a constant to predict the depth of carbonation of structures built with differing strength grades of concrete in a severe environment like Kuwait. The paper recommends that concrete structures located in hot dry coastal regions should be built with a compressive strength, at least in the range of 30–50 MPa, in order to avoid premature durability problems.

The carbonation of concrete structures in the tropical environment of singapore and a comparison with published data for temperate climates

The carbonation depths and compressive strengths of four reinforced concrete buildings which ranged in age from 7 to 59 years were measured in the tropical environment of Singapore. The average carbonation depths, d, were related to the age o of the building by the relationship d = KVage, where the carbonation constunt, K, Was approximately 7 mm/(year)1/2. For anv given structure the ratio of the maximum to average carbonation depth varied from 2·1 to 2·8. The carbonation depth and K value were also dependent on the quality (compressive strength) of the concrete, concrete with compressive strengths > 20 MPa showing lower carbonation depths and K-values than concrete with compressive strengths < 20 MPa. The K-values measured in this study, 5·5–8·6 mm/(year)1/2 were generally higher than those reported for temperate climates (1–3 mm/(year)1/2). The difirences are attributed to (i) the generallv lower grade (compressive strength) of the concrete used in the construction of the buildings and (ii) the signijicantlv higher mean dai1y temperature in Singapore, 27°C, compared to the temperate climates, 8° to 9°C.

Carbonation of concrete structures and decomposition of CSH

The paper discloses the fact that phenomenon of CSH in hardened cement paste being decomposed through carbonation to be altered into CaCO 3, SiO 2 and H 2O have been occurring widely in various types of concrete structures. The zones in concrete structures where such phenomenon have occurred coincide approximately with the zones which remain uncolored in coloration reaction using phenolphthalein, and moreover, the zones when compared with sound zones present a coloring as if bleached, and thus can be discerned by the naked eye.