Technique to Produce Recycled Aggregate Concrete with Crushed Concrete Waste
Takehiro SAWAMOTO and Masanori TSUJI
Abstract:Concrete waste is hardly recycled to be aggregate for concrete by only normal crushing, because the micro cracks remain in the crushed concrete and the particles of only mortar or cement paste are included. Thus many techniques to produce recycled aggregate are proposed and practiced, but these techniques need significantly much energy and may generate much CO2 . As the preliminary test results, it was clarified that processes for recycled aggregate to absorb water or Pozzolanic material can improve the strength of recycled aggregate concrete, even though the only crushed concrete wastes are used. This absorbed water or Pozzolanic liquid is expected to fill up the micro cracks in recycled aggregate with cement gel by cement hydration or Pozzolanic reaction. Process to soak aggregate in mixing water was tried in the preliminary test for recycled aggregate to absorb water, but this process takes more than 10 minutes. On the other hand, attendance of colloidal silica as a Pozzolanic material into mixing water caused smaller slump. In this paper, the process to soak the recycled aggregate in colloidal silica solution before mixing is evaluated to sustain slump of plain concrete, and also the application of agent for reducing surface tension of mixing water is investigated to cut off the soaking process that is for aggregate to absorb enough water during mix. Key Words:Recycled aggregate, Concrete, Colloidal silica, Drying shrinkage reducing agent, Concrete waste, Recycle