**3. Mixture proportions design**

This section principally introduce that a local mixture proportion method in Taiwan, densified mixture design algorithm (DMDA), is employed to design and prepare the cement-based composite for producing the cold-bonding recycling coarse aggregates, the logic and procedure of DMDA, how to design mixture proportions of cold-bonding recycling coarse aggregates by utilization of DMDA, and the mixture proportions of coldbonding recycling coarse aggregates.

#### **3.1 Design logic of densified mixture design algorithm, DMDA**

The densified mixture design algorithm (DMDA) was developed by National Taiwan University of Science and Technology since 1992 is a mixture proportion method for cementbased composite (e.g. mortar, plain concrete, high performance, self-consolidating concrete and so on), in which the paste volume method and the current dry loose density (i.e. unit weight) method are incorporated together for obtaining the optimized cement paste through densely packing aggregates (Chang et al., 2001; Tsai, 2005; Tsai et al., 2006). The most important design logic of DMDA is the achievement of "least void" through the utilization of fly ash (to fill the void between blended aggregates) and the cement paste (to fill the rest of the void). The utilization of fly ash (in addition to the cement paste) to fill the void between blended aggregates will increase the density of cement-based composite (Tsai et al., 2006). And the addition of the super plasticizers (SP) is helpful to solve the potential problem of tangling or balling of fibers (Tsai et al., 2009, 2010). Thus the workability of the cement-based composite with the aid of SP is ensured as a result.

#### **3.2 Design consideration of cold-bonding recycling aggregate**

In conventional mixture design, the cement-based composite workability is decided by the water amount and the compressive strength whereas the durability is decided by the waterto-cement ratio (w/c) (American Concrete Institute [ACI], 1991). The workability can be improved by increasing the water amount (Neville, 2000) and the strength can be increased by increasing the cement content. However, too much cement paste will cause chemical shrinkage, and the shrinkage rate or expansion rate is in direct proportion to the water and cement amount due to the hydration of the cement (Hwang & Lu, 2000; Mather, 2000). Besides, ordinary cement-based composite contains water at least 20 % by its volume, and hence drying shrinkage will be unavoidable. So the durability of cement-based composite is

This section principally introduce that a local mixture proportion method in Taiwan, densified mixture design algorithm (DMDA), is employed to design and prepare the cement-based composite for producing the cold-bonding recycling coarse aggregates, the logic and procedure of DMDA, how to design mixture proportions of cold-bonding recycling coarse aggregates by utilization of DMDA, and the mixture proportions of cold-

The densified mixture design algorithm (DMDA) was developed by National Taiwan University of Science and Technology since 1992 is a mixture proportion method for cementbased composite (e.g. mortar, plain concrete, high performance, self-consolidating concrete and so on), in which the paste volume method and the current dry loose density (i.e. unit weight) method are incorporated together for obtaining the optimized cement paste through densely packing aggregates (Chang et al., 2001; Tsai, 2005; Tsai et al., 2006). The most important design logic of DMDA is the achievement of "least void" through the utilization of fly ash (to fill the void between blended aggregates) and the cement paste (to fill the rest of the void). The utilization of fly ash (in addition to the cement paste) to fill the void between blended aggregates will increase the density of cement-based composite (Tsai et al., 2006). And the addition of the super plasticizers (SP) is helpful to solve the potential problem of tangling or balling of fibers (Tsai et al., 2009, 2010). Thus the workability of the

In conventional mixture design, the cement-based composite workability is decided by the water amount and the compressive strength whereas the durability is decided by the waterto-cement ratio (w/c) (American Concrete Institute [ACI], 1991). The workability can be improved by increasing the water amount (Neville, 2000) and the strength can be increased by increasing the cement content. However, too much cement paste will cause chemical shrinkage, and the shrinkage rate or expansion rate is in direct proportion to the water and cement amount due to the hydration of the cement (Hwang & Lu, 2000; Mather, 2000). Besides, ordinary cement-based composite contains water at least 20 % by its volume, and hence drying shrinkage will be unavoidable. So the durability of cement-based composite is

Specific gravity 1.09 Water reduction (%) 30.00 Solid content (%) 25.70 pH value 2.81

Item

Table 6. The characteristics of carboxylate-based superplasticizer.

**3.1 Design logic of densified mixture design algorithm, DMDA** 

cement-based composite with the aid of SP is ensured as a result.

**3.2 Design consideration of cold-bonding recycling aggregate** 

**3. Mixture proportions design** 

bonding recycling coarse aggregates.

destroyed due to disintegration and crack formation. To avoid these problems cement-based composite mixture designed with low water amount and low cement content is proposed.

Durability design should be considered for improving both the fresh and hardened stages of the cement-based composite and should finally extend their service life. First and foremost the cement-based composite mixture design should have a very low water amount (Neville, 2000) so as to minimize the shrinkage rate or the expansion rate (Hwang & Lu, 2000). Then, the cement-based composite must be designed to satisfy the construction needs such as with zero or low slump for cold-bonding recycling aggregate or roller compacted concrete, with high slump for self- consolidating concrete or high performance concrete, type of construction work, and the required final finished result. In plastic stage, the cement-based composite is designed to prevent the occurrence of plastic shrinkage cracks due to excess water evaporation from its surface. A certain amount of fibers should be included in the cement-based composite to absorb energy and in the case of crack formation, to stop their propagating (Rossi et al., 1987). The addition of pozzolanic materials (i.e. BF slag and fly ash) is necessary to help the self-healing of cracks if they are generated (Tsai et al., 2009). A strict standard operation procedure for mixture proportion, material selection, trial batch, quality control and curing are required to lower the possibility of crack formation.

The DMDA was adopted to design the intended cement-based composites for producing the cold-bonding recycling coarse aggregates. In order to minimize the shrinkage rate or the expansion rate and ensure the durability of cold-bonding recycling coarse aggregate, a very low water-to-cementitious ratio of 0.20 was selected to design mixture proportions of cement-based composite. And a total of 39.4 kg glass fibers (the volume=0.02 m) was added to reach the intended design value of 2.0 % by volume of the cement-based composite for preventing such cracks and enhancing the toughness as well as volume stability (Rossi et al., 1987; Tsai et al., 2009, 2010) of cold-bonding recycling coarse aggregate. In view of cement has the most energy consumption and CO2 emission in all constituent materials of cold-bonding recycling coarse aggregate as well as the abovementioned disadvantages, the amount of cement is limited to less than 200 kg/m3. There were three various amount of cement (i.e. 50, 100 and 200 kg/m3) designed for every recycling resource to magnify the application cold-bonding recycling coarse aggregates in the future.
