Effects of Recycled Aggregate Grading on Engineering Properties of Concrete

• Main Authors: Tzong-Ruey Yang, 楊宗叡
• Other Authors: Ta-Peng Chang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/67137848270001910780

碩士 === 國立臺灣科技大學 === 營建工程系 === 96 === This paper, studied the engineering properties of recycled coarse aggregate and recycled concrete following the regulation specified in the “Draft of Construction Specification for Recycled Concrete” of Taiwan. Four kinds of coarse aggregate, natural aggregate, recycle aggregate from lab, recycle aggregate from field and brick, were used to manually produce the H- and N- classes recycled aggregate. For the experiment work on the mechanical properties of concrete, pozzolanic materials were added according to the common mixture proportion used by commercial ready mixed concrete plants. The water-to-cementious materials ratios (w/c) were controlled to be 0.3 and 0.6. The elastic moduli of N-class recycled aggregate were investigated by change the volume ratios of recycled coarse aggregate to total aggregate and calculated by the theory of composite materials. Research results show that: (1) Following the grading specified in the “Draft of Construction Specification for Recycled Concrete”, the crushing strength of H-class recycled aggregate is between 7.56 ~13.35MPa; and N-class recycled aggregate is between 3.41 ~5.43MPa. The strength difference results from different low specific weight and high absorption property of different recycled aggregates. (2) Same as normal concrete, recycled concrete with low w/c ratio obtains higher compressive strength. The compressive strengths also vary with the grading of H-and N-class aggregate. For example, the compressive strength of RH206 is 30.11 MPa, and 28.05 MPa for RN206 at age of 56 days. It revealed that the “Draft of Construction Specification for Recycled Concrete” is conscientious and conservative since the compressive strengths of all specimens were higher than those specified in the regulation of C-class recycled concrete. (3) The thermal conductivity of recycled concretes were not changed with ages, but varied with grades and content of recycled aggregate. For example, at the w/c ratio equal to 0.3, the thermal conductivity is 2.23 W/m•k for concrete mixed with RH2 aggregate,1.93 W/m•k with RN2 aggregate. When the recycle aggregate content was changed from 40% to 60%, the thermal conductivities were varied from 2.06 to 1.68 W/m•k. (4) The Elastic modulus of recycled concrete is decreased with the increase of recycled aggregate content and varied with aggregate grade. For example, at the w/c ratio equals to 0.3 concretes mixed with RN2 recycled aggregate, with the content changed from 40% to 60%, the elastic modulus of concretes were varied from 27.44 to 20.73 GPa. The loss ratios of elasticity modulus between RH1 and RN1 are 16.24% to 32.63%. (5) Using the theory of composite material (Yang’s Model) to estimate elastic modulus of recycled aggregate, the elastic modulus of concrete with RH1 aggregate is 41.28 GPa and the elastic moduli of concrete with N class aggregate are varied from 10.34 to 27.86 GPa.