Effect of partial replacement of fine aggregate by internal curing materials on mechanical properties of concrete

Internal curing has long been utilized to decrease self-shrinkage and consequently the increased danger of concrete cracking prematurely. The measured mechanical characteristics of concrete were studied in five mixes, both with and without internal curing. Two of these mixtures have a 10% replacement rate, with one using ceramic and the other Attapulgite, while the other two have a 20% replacement, with one using ceramic and the other using Attapulgite, and the fifth is a reference mixture with no replacement for comparative reasons. With an increase of 27.93%, the ceramic combination with a 20% replacement rate is judged to have the highest compressive resistance, followed by the Attapulgite mixture with a 20% replacement rate with an increase of 34.2%. The results showed that the ceramic and Attapulgite internal curing purposes were highly effective, especially with a 20% replacement. The use of crushed ceramics and attapulgite as internal curing materials improves the characteristics of concrete.

Estimation of Rheological Effects in Cantilever Concrete Bridges on the Basis of a Span's Deflection Line

A characteristic feature of bridges as large span objects made using cantilever concreting technology are their excessive deflections, which are a result of rheological processes in concrete and pre-stressing steel. These deflections can be caused by the destruction of the material, e.g., concrete cracking, as well as the changing of the static scheme of the bridge structure, such as the subsidence of supports. The purpose of the work is to determine internal forces based on the deformation of a span. An algorithm for the correction of the deflection function, which is determined from geodetic measurements with a low accuracy, was proposed. It is characterized by a marked improvement in the results of calculations and, to a small extent, leads to the smoothing of the original measurement results. The algorithm is adapted to the analysis of a selected fragment of the structure, e.g., spans with the largest length and can be useful for monitoring bridge structures.

Microorganism, Carriers, and Immobilization Methods of the Microbial Self-Healing Cement-Based Composites: A Review

Low tensile strength, poor elastic modulus, and complex concrete cracking work condition are almost unavoidable due to the intrinsic brittleness. To deal with concrete maintenance and durability, microbial self-healing concretes have been rapidly developed and widely applied recently. The microbial self-healing can specifically patch fractures as well as boost the concrete structure’s capacity, durability, and permeability. This paper presents the state-of-the-art in the microbe induced self-healing in cement-based composites. The microorganism and carriers were classified according to the working theory and repair effects. Additionally, the precise efficiency and effect of various technologies are also evaluated for microbial immobilization. Based on the literature review and summary from the perspective of microorganism, carriers, and immobilization methods, challenges and further works are discussed.

Study on Concrete Cracking Caused by Non-Uniform Corrosion of Steel Bar

In this paper, the cracking of concrete cover caused by steel bar corrosion was discussed and studied based on the three-period model of steel bar corrosion in concrete. In the analysis, according to the non-uniformity of steel bar in reinforced concrete under natural environment, the contour of corrosion layer is simplified into a semi-ellipse. The steel bar corrosion was divided into three different periods by two corrosion points, namely, the void to be filled was exactly filled and the concrete cover was exactly cracked. Different model assumptions are made for each corrosion period. Before the concrete cover cracks, it is developed into an elastic plate. Based on the theory of elastic mechanics, the maximum corrosion depth of steel bar when concrete cover cracks is predicted.....