Fundamental Issues Towards Unified Design Theory of Recycled and Natural Aggregate Concrete Components

In the past 20 years,recycled aggregate concrete(RAC),as a type of low-carbon concrete,has become a worldwide focus of research.However,the design methodology for RAC structural components remains a challenge.Consequently,demands for a unified design of natural aggregate concrete(NAC)and RAC components have been presented.Accordingly,this study analyses the necessity of a unified design theory and provides an in-depth demonstration of the strength determination,compressive constitutive relationship,and design method of concrete components.The coefficient of variation of RAC strength is found to be generally higher than that of NAC strength.The compressive and tensile strengths of RAC can be defined and determined using the same method as that used for NAC.The uniaxial compressive constitutive relationship between NAC and RAC has a unified mathematical expression.However,the elastic modulus of RAC decreases,and its brittleness exhibits an increasing trend compared with that of NAC.Finally,to unify the design formulae of RAC and NAC components for bearing capacity,modification factors for RAC components are proposed considering safety and reliability.Additionally,the feasibility of the proposed unified time-dependent design theory is demonstrated in terms of conceptual design and structural measures considering the effects of strength degradation and reinforcement corrosion.It is believed that this study enriches and develops the basic theory of concrete structures.

Proposing a development framework for sustainable architecture, engineering, and construction industry in China: Challenges, best practice, and future directions

China’s architecture,engineering,and construction(AEC)industry needs a clear and sustainable development roadmap.Drawing inspiration from speeches delivered at a seminar hosted by the Chinese Academy of Engineering and extensive literature research on Chinese policies,this article presents a summary of the current trends in the AEC industry in four dimensions:industrialization as the foundation,intelligence as the enabler,lean management as the strategy,and green development as the goal.These four dimensions are intricately interconnected and rooted in multiple disciplines.The article provides a detailed review of the current practices,challenges,and future directions associated with each dimension.Additionally,ten grand challenges were proposed to stimulate discussions on the future of the AEC industry.This article offers an overarching understanding of the AEC industry and presents a four-dimension framework for sustainable development,which can be valuable for AEC practitioners.

Impact assessment of river sand resource shortage under different policy scenarios in China

More than half of the annual global concrete materials were produced in China due to the rapid developing construction industry,which partly led to the shortage of river sand.However,mining rate exceeds the natural replenishment rate of river sand recently,resulting in depletion of natural river sand accumulation.The increasing demand of river sand influences lots of aspects including altered landforms,increasing carbon emissions,ecological deterioration,international trades and disputes.To face the river sand resource shortage in China and to propose possible coping strategies,the data of river sand for construction in China and other related data were collected,and it is suggested that effective policy measures should be taken right now to protect river sand and strictly manage sand mining.Professional solutions for river sand shortage can be summarized as“5Rs”principle,which includes reduce,recycle.reuse,replace and recover.System dynamic model is established to predict the trend of river sand shortage and it was predicted that the gap between river sand supply and demand will come up to 63%.The impact of three policy scenarios is tested in the model,and the gap can be reduced to 35%by single policy scenario,while the scenario with all policy measures is able to reduce the contradiction between supply and demand to 4%.Suggestions are proposed from the aspects of structural and material technology,policy measures and international alliances.Attention should be paid to the shortage of river resources,to realize the sustainable development of the construction industry and other related industries,and to promote the harmonious coexistence of human and nature.

Editorial:Low-carbon Materials and Green Construction

Dear colleagues,Welcome to the inaugural issue of Low-carbon Materials and Green Construction(LMGC).This journal is a new international journal concerned with the materials and construction in civil engineering to cope with the challenges raised by climate change,together with resources and energy consumption,which is dedicated to the widest dissemination of high-quality original research and insights.

混凝土结构低碳设计理论前瞻

国家“双碳”战略和建筑业低碳发展共识,呼唤混凝土结构的低碳设计理论,本文通过简述混凝土行业低碳转型的历史与趋势,提出气候变化挑战下混凝土结构-环境共生系统的设计新需求;在混凝土结构-环境动态耦合关系的量化表征中,剖析了低碳设计从考虑可持续性的结构可靠性设计,到以双向设计为特征的结构可持续性设计的演进,将现有混凝土结构可持续性相关分析与设计方法融入低碳设计范畴,为气候变化下混凝土结构生命周期内的低碳排放与可靠服役性能提供保障;为实施低碳设计调控,结合本团队十余年的理论探索与实践,构筑混凝土结构3R^+(C)减碳技术体系,挖掘现有典型低碳技术的减排潜力与推广前景,进一步,提出未来研究方向与建议,推动混凝土结构低碳设计创新发展与应用。