Effect of microlimestone on properties of self-consolidating concrete with manufactured sand and mineral admixture

Self-consolidating concrete(SCC)with manufactured sand(MSCC)is crucial to guarantee the quality of concrete construction technology and the associated property.The properties of MSCC with different microlimestone powder(MLS)replacements of retreated manufactured sand(TMsand)are investigated in this study.The result indicates that high-performance SCC,made using TMsand(TMSCC),achieved high workability,good mechanical properties,and durability by optimizing MLS content and adding fy ash and silica fume.In particular,the TMSCC with 12%MLS content exhibits the best workability,and the TMSCC with 4%MLS content has the highest strength in the late age,which is even better than that of SCC made with the river sand(R sand).Though MLS content slightly affects the hydration reaction of cement and mainly plays a role in the nucleation process in concrete structures compared to silica fume and fly ash,increasing MLS content can evidently have a significant impact on the early age hydration progress.TMsand with MLS content ranging from 8%to 12%may be a suitable alternative for the Rsand used in the SCC as fine aggregate.The obtained results can be used to promote the application of SCC made with manufactured sand and mineral admixtures for concrete-based infrastructure.

Effects of carbon-sequestering coral aggregate on pore structures and compressive strength of concrete

CO_(2)sequestration/storage shows considerable impacts on the pore structures and compressive strength of concrete.This paper presents a study in which coral aggregates were presoaked in Ca(OH)_(2) slurries with different solid-to-liquid ratios(i.e.0.2,0.4,and 0.6 g/mL)followed by accelerated carbonation.The effects of CO_(2)sequestration on the particle size distribution,cylinder compressive strength,water absorption,and apparent density of coral aggregate were investigated.The evolution of pore structures in coral aggregate concrete after CO_(2)sequestration was also studied.Additionally,the effect of CO_(2)sequestration on the development of compressive strength of coral aggregate concrete was explored.The results showed that CO_(2)sequestration affected the properties of coral aggregate.Moreover,the porosity of CaCO_(3) formed by CO_(2)sequestration was the highest in the concrete.With the increase of solidto-liquid ratio,the porosity of cement pastes and the CaCO_(3) increased,and more big pores existed in the cement pastes and CaCO_(3).Furthermore,the compressive strength of coral aggregate concrete when the solid-to-liquid ratio was 0.2 g/mL increased compared with that before CO_(2)sequestration,but the compressive strength reduced when the ratio increased to 0.6 g/mL.

Novel empirical model for predicting residual flexural capacity of corroded steel reinforced concrete beam

In this study,a total of 177 flexural experimental tests of corroded reinforced concrete(CRC)beams were collected from the published literature.The database of flexural capacity of CRC beam was established by using unified and standardized experimental data.Through this database,the effects of various parameters on the flexural capacity of CRC beams were discussed,including beam width,the effective height of beam section,ratio of strength between longitudinal reinforcement and concrete,concrete compressive strength,and longitudinal reinforcement corrosion ratio.The results indicate that the corrosion of longitudinal reinforcement has the greatest effect on the residual flexural capacity of CRC beams,while other parameters have much less effect.In addition,six available empirical models for calculating the residual flexural strength of CRC beams were also collected and compared with each other based on the established database.It indicates that though five of six existing empirical models underestimate the flexural capacity of CRC beams,there is one model overestimating the flexural capacity.Finally,a newly developed empirical model is proposed to provide accurate and effective predictions in a large range of corrosion ratio for safety assessment of flexural failure of CRC beams confirmed by the comparisons.

社会信任与员工效率

本文理论分析并实证检验了社会信任对企业员工效率的影响及其作用机制。以中国2007—2019年沪深A股非金融上市公司为研究样本,结果发现,社会信任能显著提升企业的员工效率;社会信任对员工效率的提升作用在高学历员工占比更大,以及所处环境不确定性更高的企业显著更大。进一步的检验发现,社会信任能促使企业扩大内部薪酬差距并提高风险承担水平,且内部薪酬差距和风险承担在社会信任与员工效率之间均具有显著的部分中介效应。这表明,增强薪酬机制的激励作用和改善投资决策有效性是社会信任提升员工效率的重要作用机制。上述结论从社会信任的视角为员工效率的影响因素提供了新证据,对于加强培育优良的社会信任环境并构建以诚信为核心的企业文化以推动企业高质量发展具有重要的现实意义。