A local radial basis function collocation method for band structure computation of phononic crystals with scatterers of arbitrary geometry

A numerical algorithm based on the local radial basis function collocation method (LRBFCM) is developed to efficiently compute the derivatives of primary field quantities. Instead of a direct calculation of the derivatives by partial differentiation of the shape functions as in traditional numerical approaches, the derivative calculation in the present work is performed using a simple finite difference scheme with an introduced fictitious node. The developed algorithm is geometrically very flexible and can be easily applied to the continuity and boundary conditions of arbitrary geometries, which require an accurate derivative computation of the primary field quantities. The developed LRBFCM are applied to phononic crystals with scatterers of arbitrary geometry, which has not yet been reported before to the authors’ knowledge. A few examples for anti-plane elastic wave propagation are modelled to validate the developed LRBFCM. A comparison with finite element modelling shows that the present method is efficient and flexible

The potency of recycled aggregate in new concrete: A review

Purpose: This paper aims to review the effect of using recycled aggregates (RA) on the properties of recycled aggregate concrete (RAC) following the steady rise in global demand for concrete and the large generation of construction and demolition waste. Design/methodology/approach: This study reviewed relevant literature of research work carried out by previous researchers, leading to a deeper understanding of the properties of both RA and RAC. The properties of RA and RAC reported in the various studies were then compared to their corresponding natural aggregate (NA) and natural aggregate concrete, as well as the specifications provided in different codes of practice. In addition, the mix design methods appropriate to RAC and the cost implication of using RA were reviewed. Findings: Findings show that the contribution of RA to strength appears inferior in comparison to NA. The shortcoming is attributed to the mortar attached to the RA, which raises its water absorption capacity and lowers its density relative to those of NA. However, it has been reported that the use of regulated quantity of RA, new mixing and proportioning methods, the addition of admixtures and strengthening materials such as steel fibres, can improve both mechanical and durability properties of RAC. Cost evaluation also showed that some savings can be realized by using RA instead of NA. Originality/value: This research serves as a guide for future works and suggests that the use of RA as aggregate in new concrete is technically possible, depending on the mix design method adopted.</p

Recycled Concrete Aggregate and its Prospects in Structural Concrete

В статті досліджені теоретичні засади формування міжнародної стратегії маркетингу. Виявлені проблеми застосування міжнародної маркетингової стратегії на українських промислових підприємствах. Запропоноване удосконалене визначення поняття «міжнародна маркетингова стратегія промислового підприємства» вказує на специфічні особливості формування маркетингової стратегії промислового підприємства

Sustainable infrastructure development through use of calcined excavated waste clay as a supplementary cementitious material

Major infrastructure development projects in London produce large quantities of London clay and use significant volumes of concrete. Portland cement (CEM I) in concrete is normally partially replaced by supplementary cementitious materials such as ground granulated blastfurnace slag or pulverised fuel ash. The supply of supplementary cementitious materials is critical to the production of sustainable concrete. This study has investigated use of waste London clay as a supplementary cementitious material. The optimum calcined clay was produced at 900 °C and concrete made with 30 wt% of CEM I replaced by calcined clay had 28-day strengths greater than control samples. Compressive strengths of concrete containing calcined London clay were similar to concrete containing ground granulated blastfurnace slag and pulverised fuel ash. The production of calcined London clay emits ∼70 kg CO2/tonne and this is 91% lower than CEM I. 30 wt% replacement of CEM I by calcined London clay therefore produces concrete with ∼27% lower embodied carbon. London clay can be calcined to form a technically viable supplementary cementitious material and use of this in concrete would enable major civil infrastructure projects to contribute to a circular economy

Thermodynamic modelling of cement chemistry at high temperature

The prediction of the likely future state of cementitious materials has been the focus of research for many decades and has expanded to match the availability of computational power and of codes and data. The field has traditionally been divided into two activities and even communities; high and low temperature methods. By tradition, each community has favoured its own models, codes and data but recent developments are leaving this boundary less distinct than in the past. To compound this, is the wider adoption of methods complementary to thermodynamics, which makes modelling high temperature cement chemistry an exciting area in which to conduct research. What follows, is a very personal view of the major advances in modelling cement chemistry at high temperatures, the needs and drivers to model development and an equally personal speculation about areas of fruitful research and development in the foreseeable future.</p

Thermodynamic Cement Hydration Modelling Using HYDCEM

Thermodynamics have been successfully applied to the field of cement hydration science to predict the formation of phase assemblages and pore solution chemistry. For any cement hydration model to be accepted, it must provide accurate forecasts of which solids may form and how the cement will dissolve over time. This is particularly important for the ongoing development of new sustainable cements and understanding their hydration behaviour in service. HYDCEM is a cement hydration model that simulates volumetric changes of cement and gypsum dissolution and product growth that, up to now, assumed which solids would form. In order to improve its usefulness, the PHREEQC geochemical software has been coupled with HYDCEM to provide more sophisticated and flexible predictions of which phases may form under equilibrium conditions and generate their change in volume over time for curing temperatures between 5-45°C, variable w/c ratio and cement oxide compositions. To incorporate the coupling of PHREEQC into the model, HYDCEM was re-written in the C# programming language (previously coded in MATLAB) which also improved overall performance and functionality. This paper presents analysis of a cement system with a w/c ratio of 0.5 at a curing temperature of 20°C and provides predictions of the phase assemblage, phase and product changes in volume and heat evolution over a 1,000-day period in one hour time-steps