Applying Theories of Particle Packing and Rheology to Concrete for Sustainable Development

Concrete is one of the most important construction materials. However, it is not so compatible with the demands of sustainable development because manufacturing of cement generates a large amount of carbon dioxide and therefore cement consumption produces a huge carbon footprint. Currently, the cement consumption is generally lowered by adding supplementary cementitious materials to replace part of the cement. Nonetheless, in order to maintain performance, there is a limit to such cement replacement by supplementary cementitious materials. To further reduce the cement consumption, the total cementitious materials content has to be reduced. This requires the packing density of the aggregate particles to be maximized so that the amount of voids in the bulk volume of aggregate to be filled with cement paste could be minimized and the surface area of the aggregate particles to be minimized so that the amount of cement paste needed to form paste films coating the surfaces of aggregate particle for rheological performance could be minimized. Such optimization is not straightforward and modern concrete science based on particuology is needed. Herein, a number of new theories regarding particle packing and rheology of concrete, which are transforming conventional concrete technology into modern concrete science, are presented. These theories would help to develop a more scientific and systematic concrete mix design method for the production of high-performance concrete with minimum cement consumption

Development of Sustainable High-Strength Self-Consolidating Concrete Utilising Fly Ash, Shale Ash and Microsilica

With high flowability and passing ability, self-consolidating concrete (SCC) does not require compaction during casting and can improve constructability. The favourable properties of SCC have enabled its widespread adoption in many parts of the world. However, there are two major issues associated with the SCC mixes commonly used in practice. First, the cement content is usually at the high side. Since the production of cement involves calcination at high temperature and is an energy-intensive process, the high cement content imparts high embodied energy and carbon footprint to the SCC mixes. Besides, the exothermic reaction of cement hydration would cause high heat generation and early thermal cracking problem that would impair structural integrity and necessitate repair. Second, the strength is usually limited to around grade 60, which is considered as medium strength in nowadays achievable norm. With a view to develop sustainable high-strength self-consolidating concrete (HS-SCC), experimental research utilising fly ash (FA), shale ash (SA), and microsilica (MS) in the production of SCC has been conducted, as reported herein

Nonlinear multilevel analysis of reinforced concrete frames

Full range analysis of reinforced concrete (RC) members covering the post-crack and post-peak regimes is important for obtaining the deformation response and failure mode of structural members. When a RC member is subject to an increasing external load, the critical sections would exhibit cracking and/or softening. Due to stress relief effect in the proximity of crack opening and plastic hinging, unloading may occur at the adjacent regions. The variable stress states of discrete sections would lead to sectional variation of stiffness, which could not be accounted for by conventional structural analysis methods. In this paper, a nonlinear multilevel analysis method for RC frames whereby the frame members are divided into sub-elements and sectional analysis is utilised to evaluate stiffness degradation and strength deterioration is developed. At sectional level, the secant stiffness is determined from moment-curvature relation, where the curvature is evaluated based on both transverse displacements and section rotations of the frame member. Unloading and reloading behaviour of concrete and reinforcing steel is simulated. In implementing the multilevel analysis, secant iteration is performed in each step of displacement increment to obtain the convergent solution satisfying equilibrium. Numerical example of RC frame is presented to demonstrate the applicability and accuracy of the proposed nonlinear multilevel analysis method

Effects of Crushed Oyster Shell on Strength and Durability of Marine Concrete Containing Fly Ash and Blastfurnace Slag

A large quantity of oyster shell is generated every year in coastal regions. Instead of being dumped as waste, after crushing or grinding, oyster shell may be recycled for use in concrete. Herein, the use of crushed oyster shell (COS) in conjunction with fly ash (FA) and blastfurnace slag (BS) to produce marine concrete was studied. By varying the COS, FA and BS contents in the marine concrete, the combined effects of COS, FA and BS on the cube compressive strength, water penetration, cyclic wetting-drying chloride attack and long-term seawater attack resistances were evaluated. The results showed that the addition of proper amounts of COS, FA and BS has positive effects on the strength and durability of marine concrete, but excessive COS may have negative effects. Hence, the combined addition of COS, FA and BS up to a certain optimum COS content is a promising way of producing a higher performance and greener marine concrete

A rigorous analytical model for shrinkage cracking of reinforced concrete

published_or_final_versio

Waist circumference and waist-to-height ratio of Hong Kong Chinese children

<p>Abstract</p> <p>Background</p> <p>Central body fat is a better predictor than overall body fat for cardiovascular (CV) risk factors in both adults and children. Waist circumference (WC) has been used as a proxy measure of central body fat. Children at high CV risk may be identified by WC measurements. Waist-to-height ratio (WHTR) has been proposed as an alternative, conveniently age-independent measure of CV risk although WHTR percentiles have not been reported. We aim to provide age- and sex-specific reference values for WC and WHTR in Hong Kong Chinese children.</p> <p>Methods</p> <p>Cross sectional study in a large representative sample of 14,842 children aged 6 to 18 years in 2005/6. Sex-specific descriptive statistics for whole-year age groups and smoothed percentile curves of WC and WHTR were derived and presented.</p> <p>Results</p> <p>WC increased with age, although less after age 14 years in girls. WHTR decreased with age (particularly up to age 14). WHTR correlated less closely than WC with BMI (r = 0.65, 0.59 cf. 0.93, 0.91, for boys and girls respectively).</p> <p>Conclusion</p> <p>Reference values and percentile curves for WC and WHRT of Chinese children and adolescents are provided. Both WC and WHTR are age dependent. Since the use of WHRT does not obviate the need for age-related reference standards, simple WC measurement is a more convenient method for central fat estimation than WHRT.</p

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum