The article presents an overview of the environmental actions of the Danish cement and concrete industry over the last ten years. The areas include reduced Portland clinker content which means improved CO2 footprint of the concrete. It is described how carbonation of concrete after demolition and crushing may improve the CO2 footprint even further by taking into account the absorption of CO2 from the atmosphere. Recently there has been a 3-year project initiated by the Danish cement and concrete industry. This project has succeeded in promoting the image of concrete as a sustainable building material in the Danish public. It is the result of several scientific investigations for instance determining the effect of concrete emissions on the indoor air quality and the solution to hydrocarbon pollution in concrete slurry at the concrete plant. Finally the article contains examples of how to improve the sustainability of concrete production and how to produce green concrete. Green concrete is the term used in Denmark for environmentally friendly concrete production and structures.
This paper aims to establish a technique for easy concrete recycling as a solution essential for the creation of a closedloop recycling society. The technique introduced in this study enables improvement of the recovery rate of original aggregate by enhancing the peeling-off effect of aggregate without any degradation of mechanical properties. The enhanced peeling-off effect is realized by applying a surface improving agent to the aggregate. In this paper, material tests were conducted on recycled aggregates with low quality and middle quality. In the test, two types of surface improving agent, an oil-type improving agent and a silane-type improving agent, were used. The test results have shown that the recycled aggregate finished with silane-type improving agent was greatly improved in recovery rate but showed lowered strength. On the other hand, the recycled aggregate finished with oil-type improving agent was somewhat superior in recovery rate compared with non-finished aggregate. In addition the oil-type improving agent improved hardening properties. Flexural tests of reinforced concrete beams were conducted only for the oil-type improving agent. Consequently, the possible applicability of recycled aggregate finished with oil-type surface improving agent was verified.
The generation of huge amounts of construction waste is anticipated due to the demolition of older structures such as power stations built more than 30 years ago. On the other hand, the reuse of construction waste is highly essential from the viewpoint of Life Cycle Assessment (LCA) and effective recycling of construction resources. In order to promote the reuse of construction waste, it is necessary to achieve three basic concepts: (1) assurance of safety and quality, (2) decrease of environmental impact, and (3) increase of cost effectiveness of construction. This paper outlines the development of a recycling system, application of recycled aggregate concrete produced by the aggregate replacing method, which is effective in reducing both cost and environmental impact from the viewpoint of LCA for concrete waste generated by the demolition of large-scale buildings such as powerhouses. Result of this study showed that recycled aggregate concrete using the aggregate replacing method can acquire sufficient quality as structural concrete and/or precast concrete products through material design based on the value of relative quality method. Moreover, with the adoption of the developed recycling system, it was confirmed possible to recycle concrete waste produced from the demolition buildings in a highly effective manner reducing both recycling cost and environmental impact.
In order to evaluate whether concrete with recycled aggregate can be applied for concrete structures, flexural loading tests of reinforced recycled concrete members were carried out. The recycled coarse aggregate and the recycled fine aggregate were produced mainly from various reinforced concrete members of a building structure as well as from 300 mm cubic concrete specimens. The properties of concrete with recycled aggregates, such as strength, Young's modulus, shrinkage, creep and shrinkage-induced stress depending on the combination of natural and recycled aggregates, curing condition, and water to binder ratio, were discussed based on a comparison with the properties of concrete with virgin aggregates. Furthermore, the flexural behavior of reinforced recycled concrete beams was also discussed through comparison with the behavior of companion virgin concrete beams in which the tension reinforcement ratio, curing condition, and water to binder ratio of concrete, are the main factors. The results indicate the mechanics-based possibility of utilizing recycled concrete for reinforced concrete structures under the proper design and within the proper limit of application.
Two approaches to solving the problem of structural design are applied and compared for a particular design problem: the traditional Deterministic-Based Structural Optimisation (DBSO) and Reliability-Based Structural Optimisation (RBSO), which incorporates probabilistic structural reliability analysis into structural optimisation. This paper focuses particularly on basic RBSO algorithm features and numerical comparisons between RBSO and DBSO algorithms for the selected design problem. The main novelty of the paper lies in the application of the RBSO approach. A sample definition of an RBSO problem (conversion from a deterministic to a probabilistic problem) and its solution are presented for the optimisation of an RC cross-section, which is subjected to combinations of normal force and bending moments. The objective function also includes, besides the total cost of the cross-section, negative environmental impacts. Numerical results for the particular data set are presented.
The effects of aggregate characteristics on the flow ability of mortar mixtures were investigated. Two types, five single-sized and three graded fine aggregate were considered. Uncompacted voids of the aggregates were measured. Flow properties of 166 mortar batches made with different aggregates, sand-to-cement ratios (s/c) and water-to-cement ratios (w/c), were evaluated using the modified ASTM C109 flow table test method. The results indicated that in addition to w/c, the content, uncompacted voids, and size of aggregate all significantly affect mortar flow ability. Generally, aggregate having higher uncompacted void content provides its mortar with a lower flow. When aggregate content was low (s/c = 1), aggregate size had little effect on the flow ability of the mortar; when aggregate content was high (s/c = 3), aggregate size significantly influenced the mortar flow ability. The mortar with graded aggregate has better flow ability than the mortar with single-sized particles. River sand provides a mortar with better flow ability when compared to limestone. A statistical model was developed to predict the flow ability of mortar. The model can also be used to study the effect of different parameters on mortar flow properties.
Mortar and concrete are composed of solid materials and water, so that all the solid material particles can be considered to be coated with an “excess water film.” In this study, the functions of this excess water film were investigated through mortar tests and solid volume percentage tests of the solid materials in mortars. It was found that the consistency of fresh mortars such as mini-slump and flow can be evaluated by the ratio of the average thickness of the excess water film to the surface-volume average diameter of the particles of cement and fine aggregate, even for various mortar mixture proportions and fine aggregate gradings. This ratio was also found to be a reliable index to determine the optimum replacement percentage when a part of the fine aggregate in mortar is to be replaced with a mineral admixture.
In recent years, interest in early age concrete cracking has increased due to its effects on the durability and performance of concrete structures. A time-dependent material model and a structural analysis method have been developed to evaluate thermal cracking behavior. To simulate such behavior at early ages, a solidified constitutive model is proposed, which is based on the solidification concept with dependence on time and strain histories. The unified numerical model consists of a Rigid-Body-Spring Network, representing the structural behavior, combined with a truss model to represent heat transfer. Wall concrete structures are analyzed to verify the solidified constitutive model and the overall approach. The proposed model results and the experimental results show reasonable agreement in terms of cracking behavior, stress distributions and structural deformations.
A theoretical study was undertaken to propose the procedure and guidelines for the design of transverse steel confinement for the potential plastic hinge regions of plain (non-fibre) and steel fibre reinforced high strength concrete columns. To achieve this, confinement reinforcement for a few selected square and circular concrete column cross sections were designed for varying concrete compressive strengths (70-100 Mpa) and axial load levels (0.15 - 0.5). Theoretical moment curvature relations were found and curvature ductility factors were computed for all the columns. An attempt has also been made to evaluate the relevant confinement requirements of the Indian Standard Code IS-13920: 1993. The results indicate that the design equations of the Code are inadequate to provide satisfactory ductility for high strength concrete columns especially at high axial load levels. However, it has been shown that the use of steel fibre reinforced concrete results in a significant improvement in the structural response of such column cross sections. A new set of refined equations have been proposed in the present study to design the confining steel of non-fibre and steel fibre reinforced high strength concrete columns, which take into account the effects of high concrete strengths and axial load levels also. The confinement reinforcement design has been made performance based by relating the required quantity of reinforcement with the ductility demand.