**1.2 Mechanism of cold-bonding technique**

Based on the purposes of green building materials (i.e. reduction of waste and CO2 footprint, energy conservation, lightening of material, and so on), it is a critical issue for building and construction department to treat the wastes properly and encourage the recycling of resources. In spite of many investigators (Chen et al., 2010; Hung & Hwang, 2007) indicate that the sintering technique has been successfully applied to recycle abovementioned resources as lightweight aggregates. But the energy consumption and CO2 emission of sintering process are too much to be extensively adopted. A new approach, the cold-bonding technique (Cai et al., 2010, 2012 & Tsai et al., 2011, 2012) incorporates the principles of the cement chemistry (Mehta, 1986; Mindess & Young, 1981) and composite material (Gibson, 1994), was developed to recycle these resources as recycling coarse aggregates. Consequently, the main difference between cold-bonding and sintering technique is the reduction of energy consumption and CO2 emission.

The cold-bonding recycling coaese aggregate was regarded as a fiber reinforced concrete or a cement-based composite that is the original concept for developing cold-bonding recycling coarse aggregates. In which cement, blast-furnace slag (BF slag), and fly ash are regarded as cementitious materials or binders, the construction residual soil, granite or lime sludge is as a filler (i.e. aggregate), and the glass fiber is as a reinforcement. In view of the fundamental principle of concrete materials (Dowling, 1993; Skalny & Mindess,

Cold-Bonding Technique – A New Approach to Recycle

Innocuous Construction Residual Soil, Sludge, and Sediment as Coarse Aggregates 99

(a) B2-3 in original state (b) B2-3 in oven-dry state (c) B2-3 with moisture of 10.0 %

(d) B3 in original state (e) B3 in oven-dry state (f) B3 with moisture of 14.0 %

(g) B4 in original state (h) B4 in oven-dry state (i) B4 with moisture of 14.0 %

(j) B6 in original state (k) B6 in oven-dry state (l) B6 with moisture of 14.0 %

In which B2-3, B3, and B4 categories were provided from a local collecting plant of construction wastes in Tainan as well as the construction residual soil of B6 category was acquired from a construction site near Shida Road in Taipei, Taiwan. For engineering purposes, these construction residual soils of B2-3, B3, B4, and B6 categories were classified as SP (i.e. poorly graded sand), ML (i.e. silt), SM (i.e. silty sand), and CL (i.e. lean clay), respectively according to Unified Soil Classification System (ASTM, 2006). Their specific

Fig. 2. Photos of four construction residual soils in various moisture states.

gravity as well as chemical compositions are shown in Tables 4.

1989) that is the higher packing density of component materials of concrete, the higher will be the properties of concrete. To ensure characteristics of cold-bonding recycling coarse aggregates are acceptable, the cement-based composites were granulated as the recycling coarse aggregates with a higher stress of greater than 28 MPa after proportioning and mixing. These mixture proportions and conditions of granulation will be illustrated in subsequent sections.
