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Early-age thermal cracking and delayed ettringite formation (DEF) are short-term and long-term major issues to the durability of mass concrete and require a high level of consideration in the development of a suitable concrete mix design in placement and curing strategies, particularly in mixes of high cement content. Where DEF risk proves to be significant, contractors are required to adopt risk mitigation strategies including lowering concrete's temperature during placement by adding cool water or ice, for example, to the mix, embedding cooling pipes in the cast element and/or sequential placement of the concrete. These strategies can be implemented at different levels, as needed, to minimise the risk of cracking and DEF. Determining the most suitable and cost-efficient risk mitigation strategy, however, together with its implementation, is a complex task that requires consideration of each complex strategy under project-specific conditions. While a significant research effort has been invested to develop an improved understanding of the effectiveness of different early age thermal cracking and DEF risk mitigation strategies, the lack of reliable models capable of simulating and comparing the effectiveness of all scenarios remains elusive and considerably limits the ability of the practitioners in identifying the optimal approach. This paper presents a Multiphysics model developed to predict the effect of early-age thermal cracking and DEF risk mitigation scenarios. The model is validated using four real-life project Case Studies and is demonstrated to provide reliable results. In addition, the paper studies the comparative effectiveness of key risk mitigation strategies and the important parameters influencing their effectiveness.

Early-age thermal cracking and delayed ettringite formation (DEF) are major durability risks associated with mass concrete casting with high cement content. Among various strategies to mitigate the risk of early-age thermal cracking and DEF, concrete mix optimisation is favoured by the industry due to its minimal required operational adjustments and insignificant implementation cost. The existing concrete mix design optimization methods are, however, incapable of accounting for the risk of early-age thermal cracking and DEF; and have been designed solely to meet the mechanical performance targets. Mitigating the risk of DEF could be challenging mainly because limiting the temperature rise in concrete requires moderating the hydration heat/rate to minimize the risk of early-age thermal cracking and DEF which could contradict the traditional objectives associated with the concrete's mechanical performance. Further, early-age thermal cracking can be influenced by project-specific factors including the dimensions of the concrete element, ambient conditions, and external restraints which do not come into the picture in a conventional mix design approach. These issues add to the complexity of the mix design problem. This paper presents a mix design approach based on integrated numerical simulation of heat transfer in concrete and genetic algorithm optimisation that minimises the risk of early-age cracking within the limits specified for the mechanical performance of concrete. The results of the optimization framework applied to three case studies show a significant decrease in peak temperature, as well as the ratio of induced tensile stresses to developed tensile strength for optimized concrete mixes.

To investigate the hygroscopic behaviour of engineered timber, glued-laminated (glulam) timber made of Pacific Teak (Tectona grandis), Tasmanian Oak (Eucalyptus regnans/obliqua/delegatensis), Blackbutt (Eucalyptus pilularis), Radiata Pine (Pinus radiata) and Slash Pine (Pinus elliottii) and laminated veneer lumber (LVL) made of Radiata Pine were exposed to sorption and desorption cycles at two temperatures (i.e. 15 and 50 °C) and the shrinkage and swelling of samples were measured in three orthogonal directions. The samples were conditioned in different relative humidity to produce eight intermediate moisture contents (reading points) between the oven-dried and saturated states. A bilinear model was fitted to the swelling/shrinkage strain-moisture content data to accurately determine the Coefficient of Moisture Expansion (CME) and Moisture Contraction (CMC), and Coefficient of Thermal Expansion (CTE), as well as the Fibre Saturation Point (FSP) for each group of specimens. The experimental results demonstrated a significant difference in swelling/shrinkage behaviour of large glulam and LVL samples compared to small clear wood samples as well as a significant effect of temperature on moisture-induced swelling/shrinkage of glulam and LVL beams in the transverse direction. The CME and/or CMC in the transverse direction were found to decrease with increasing temperature, while swelling/shrinkage coefficients in the longitudinal direction exhibited an opposite pattern. The results of this study can potentially improve the accuracy of the hygro-thermo-mechanical and long-term analysis of glulam and LVL members.

Among different structural elements, floor elements account for the largest portion of the mass and thus the embodied energy of the structures. Therefore, a viable approach to reduce the embodied energy of buildings may involve replacing the conventional floor systems with alternative low embodied energy floor systems. This paper investigates the potential reductions in the life cycle energy of the steel structures achievable through the adoption of steel-timber composite (STC) elements as floor and shear wall systems. Evaluating the life cycle energy implications of adopting STC elements is especially important due to the trade-off between their positive and negative effects on embodied energy and operating energy, respectively, when compared to alternative conventional elements with a higher thermal mass including concrete and steel elements. The life-cycle energy of four different structures designed for a building is evaluated by accounting for energy use in material extraction and processing, component manufacturing, transportation, construction, operation and end of life phases. Two steel structures with STC and steel-concrete composite floors and concrete shear walls are considered to evaluate the effects of STC floors on the energy-usage footprint. The third structure is designed with STC floor system and CLT shear walls; and the fourth structure is designed as a concrete structure to provide a basis for comparison between energy footprint of steel structures with STC and reinforced concrete structures. The results indicate that when designing the building with a steel structure, adoption of STC floor and shear wall systems resulted in 107.5% decrease in the embodied energy at the expense of only a slight increase in the operating energy. Furthermore, adopting a steel structure with STC floors was found to result in considerable life cycle energy savings, viz. 895 MJ/m2, when compared with the same building designed with a concrete structure.

Due to their recyclability and considerably lower embodied carbon, timber floors are advocated extensively as a more sustainable alternative to concrete slabs. Cross-Laminated Timber (CLT) is an engineered wood product with low variability in mechanical properties and therefore of high reliability and quality, presenting a very attractive alternative to concrete slabs. Replacing the reinforced concrete slabs in conventional steel-concrete composite with an engineered timber product (such as CLT) leads to a significant reduction in the overall weight of the floors, and consequently the weight of supporting structural elements including columns and beams. The combination of light CLT panels and steel may allow an increase in the load-carrying span of the floor systems which is highly desirable from an architectural viewpoint. However, one major drawback negatively affecting the serviceability and thus widespread adoption of such systems in practice is the high susceptibility of undesirable vibration in steel-timber composite (STC) floors under service load conditions due to low mass and damping ratio of timber slabs. This paper presents the results of a series of experimental impact hammer tests conducted to investigate the vibrational characteristics of different STC beams. Three STC beams with different shear connector types are experimentally tested to extract their natural frequencies. Numerical models are generated and validated using the results of previously performed short-term failure tests. The validated numerical models are then used to extract the linear flexural stiffness of STC beams to determine the deflection of the beams under self-weight. The experimental results are compared against results from analytical models calculating the fundamental natural frequencies of the beams. Further, the obtained dynamic indices of STC beams are evaluated based on available standard regulations.

© Springer International Publishing AG 2018. Concrete durability is to a large extent governed by the concrete resistance to the penetration of aggressive substances. One such aggressive substances, present predominantly in marine or coastal environments, is the chloride ion. Chloride in presence of water and oxygen cause corrosion and the measurement of chloride content is an important factor in the detection of early corrosion damage induced by chloride attack. However, there is currently a lack of a reliable nondestructive method to examine the chloride content of the structure in practice. This paper presents the results of an experimental study to investigate the viability of Microwave Non-Destructive Testing (MNDT) to monitor the ingress of the chloride into the concrete. The variations in the electromagnetic properties of mortar specimens with variations in their chloride contents are measured to identify correlations between chloride content and two main electromagnetic properties of mortar; viz. dielectric constant and loss factor. EMPs are measured through two-port measurement performed using a vector network analyzer and S-band rectangular waveguide. The existence of correlations between chloride content of mortar and its electromagnetic properties is confirmed by the preliminary results, highlighting the potential for development of an MNDT technique to monitor the chloride content of concrete in practice.