دانلود رایگان مقاله انگلیسی خزش طولانی مدت و رفتار خوردگی بتن سبز طراحی شده برای تیر اصلی پل - الزویر 2018

Abstract

 Creep and shrinkage behaviors are critical factors in the precast/ prestressed concrete industry because these factors allow engineers to assess the long-term performance of concrete and to develop life-cycle estimates for concrete structures. The current study presents the results of an experimental work that addresses creep and shrinkage behaviors as well as the 20 development of compressive strength in ordinary Portland cement concrete (OPC), high performance concrete (HPC), and self-consolidating concrete (SCC). The concrete mixtures created for the present study were used to fabricate prestressed bridge girders. A conventional method (ACI) was used to design the mixture proportion for OPC and a densified mixture design algorithm (DMDA) was used to design the mixture proportions for HPC and SCC. All concrete mixtures had the same target strength of 69 MPa (10000 psi) at 56 days. Additionally, a comparative performance in terms of strength development and creep and shrinkage behaviors of ACI and DMDA concrete is performed in the present study. Test results show that all of the samples attained the target strength after 28 days of curing and that the strengths of each continued to increase afterward. Importantly, the incorporation of pozzolanic materials into concrete mixtures affected the propagation of creep strain and shrinkage positively. Furthermore, the DMDA concrete sample delivered better long-term performance than ACI concrete in terms of compressive strength, creep strain, and shrinkage.

Conclusions

The present study investigated the long-term performance of DMDA concrete (HPC and SCC) and conventional ACI concrete (OPC), including the development of compressive strength and creep and shrinkage behaviors. The following conclusions may be drawn from the results of the experiments that were conducted for the present study: 1. The compressive strength of all of the concrete samples increased with curing age. Both DMDA and ACI concretes reached their target strength after 28 days of curing rather than after 56 days, which was the time that was initially estimated. The strength of the samples continued to increase through day 120. The DMDA concrete samples exhibited greater long-term strength than the ACI concrete samples, which is attributed mainly to the pozzolanic reaction and to the filling effect of the pozzolanic materials, which were introduced via the DMDA mix design technology. 2. The incorporation of pozzolanic materials in the DMDA concrete samples positively affected not only the development of compressive strength but also the propagation of creep strain and the shrinkage behavior. In particular, the inclusion of SF in the concrete mixtures enhanced compressive strength and carbonation resistance, increasing AS while reducing DS and creep strain in the samples. 3. Aggregate and water content are two important factors that were found to affect creep strain and shrinkage behavior significantly. Particularly, increasing the aggregate content decreased creep strain and shrinkage in samples, while the opposite trend was observed for samples with higher water contents in their concrete mixtures.