State of the Art Review of Reinforcement Strategies and Technologies for 3D Printing of Concrete

This state of the art review paper aims to discuss the results of a literature survey on possible ways to reinforce printed concrete based on existing reinforcement strategies. Just as conventional concrete, for 3D printed concrete to be suitable for large-scale construction, reinforcement is needed to increase the tensile capacity of concrete members and reduce temperature and shrinkage cracking. Despite efforts that are currently underway, the development of proper reinforcement suitable for printed concrete is still very active on the research agenda. As an initial step for designing suitable reinforcement for printed concrete, the existing reinforcement methods for printed concrete as well as conventional cast concrete from the literature are reviewed and summarized. Through the preliminary evaluation of the suitability and effectiveness of various reinforcement methods, guidelines are proposed to better understand possible solutions to reinforce printed concrete and inspire new practical ideas to fill the current technology void. The conclusions also include the possible improvements of the existing reinforcement methods to be considered in future applications.

Effects of Aging on the Dry Shrinkage Cracking of Lime Soils with Different Proportions

In this study, the reasonable aging time of lime soils with different ratios was determined to investigate the effect of aging on the internal mechanism of the dry shrinkage cracking of lime soil. To this end, the effects of aging time, lime content, and particle size on the volume crack rate, expansion and shrinkage rate, particle size distribution, and pH were analyzed using a dry–wet cycle, screening, and pH tests. In addition, the changes in the particle structure of the samples and the formation of new substances were analyzed. The results revealed that the volume crack and expansion shrinkage rates of the sample initially decreased, and then stabilized with increasing aging time. In addition, the aging time of the sample increased with increasing lime content and particle size. Further, at the initial aging stage, the volume crack and expansion/shrinkage rates of the sample increased with increasing lime content and particle size. With an increase in the aging time, the pH increased and then decreased significantly to 0.57–1.1% at the reasonable aging time. These indicate that the pH exhibited a significant effect on the reasonable aging time, and this will provide useful insights for the restoration of lime soil sites.

Early-Age Thermal-Shrinkage Cracking in Deep Foundations

With the growing rate of urbanisation, deep foundations are playing an ever-larger role in the development of cities, reaching deeper than before to fulfil the requirements of new constructions. While current European standards include design procedures for structural and geotechnical design, they lack provisions for massive deep foundations with regard to early-age thermal effects. This paper presents aspects of the phenomenon especially important for deep foundations and discusses normative requirements that influence their thermal behaviour. Further, the paper describes the methods and results of the research carried out in the United Kingdom on 1.50-m-thick diaphragm walls of a deep circular shaft. Shaft features are described, as well as the materials used. The measurements were carried out using vibrating wire strain gauges coupled with temperature readings. The results presented refer to one of the test panels concreted in January 2020. The temperature results are analysed together with the influence of work scheduling on the readings. Strain results that indicate contractive behaviour of the test panel are investigated together with the possible causes leading to such readings. Plans and directions for future research are discussed.

Effects of Different Expansive Agents on the Properties of Expansive Cementitious Materials

Cracking happens in the case of restricted volumetric shrinking in cementitious materials which has a negative influence on the mechanical characteristics and longevity of concrete materials and hence, reduces the life of concrete structures. Many techniques have been developed to reduce the shrinkage cracking of concrete among which, usage of expansive agents (EA) has been utilised for decades. Different types of EA creates divergence due to its chemical characteristics. In this paper, three main categories (CaO, MgO & Sulphoaluminate based) EA have been reviewed based on four criteria of concrete structures, such as strength, expansibility, durability and flowability. The review clearly indicates that CaO-based EA boosts the strength but unable to control the temperature rise, which results in thermal cracking in the long run. While MgO-based EA is vastly used in China and Sulphoaluminate based EA have been industrially used worldwide for decades, both of these agents can successfully compensate thermal shrinkage while maintaining adequate mechanical strength and durability. Beside all this differences, all types of EA have been reported to decelerate the flowability of the concrete.

Study of Light Weight Fibre Reinforced Concrete by Partial Replacement of Coarse Aggregate with Pumice Stone

As the demand for the structural members application in the concrete industry is continuously increasing simultaneously many a times it is required to lower the density of concrete enabling light weight which helps in easy handling of the concrete and its members. In this research an experimental endeavour has been made to equate conventional concrete with light weight by partially substituting the coarse aggregate with the pumice stone aggregate in M30 grade mix design. Simultaneously small fibres of Recron3's Polypropylene have been applied to the concrete as a reinforcing medium to minimize shrinkage cracking and improve tensile properties. The coarse aggregate was substituted by the pumice aggregate in 10, 20, 30, 40, and 50 percent and fibres respectively in 0.5, 1, 1.5, 2 and 2.5 percent. The experiment is focused on strength parameters to determine the most favourable optimum percent with respect to conventional concrete. Keywords: OPC (Ordinary Portland Cement)1, FA (Fine Aggregate)2, CA (Coarse Aggregate) 3, fck (Characteristic Compressive Strength at 28days)4, Sp. Gr (Specific Gravity)5, WC (Water Content)6, W/C (Water Cement Ratio)7, S (Standard Deviation)8, Fck (Target Average Compressive Strength at 28days)9.

Effect of Silica Fume and Synthetic Fibre towards the Compressive Strength of Modified Crumb Rubber Cement Mortar

Cracking is very common problem in cement mortar. Many past research has explored the prospect of using crumb rubber (CR) to overcome this issue. Different sizes of CR have been tested to measure its effect on the pore structure and mechanical strengths of cement mortar. Hence, this study has further modified the crumb rubber mortar mix by adding silica fume and synthetic fiber to improve its mechanical properties. The experimental results suggested that the optimum silica fume replacement of cement content was 5%. Hence, for the subsequent experiment with a fixed 5%silica fume replacement, the highest compressive strength of 26 MPa was achieved with 5% crumb rubber replacement. Finally, additional 0.1% of synthetic fiber added the modified crumb rubber mix to reduce the mix brittleness has produced a desirable compressive strength close to the control specimen which was significantly higher than the minimum threshold required by the standard. However, the water content ratio for the modified mortar mix should be further investigated as the present modified crumb rubber mix has lower workability. It is envisaged that the modified crumb rubber mortar mix has a sound potential to mitigate shrinkage cracking in cement mortar.