**4.2 Optimum moisture of granulation**

In the original designing concept of cement-based composites mixture proportions for producing the recycling coarse aggregates, the recycling resources were regarded as fillers (i.e aggregates of concrete). But the natures of recycling resources are quite different from primitive aggregates (e.g. particle shape, gradation, absorption, and so on). The purpose of exploring the optimum moisture of recycling resource for granulating aggregate is to avoid two issues: 1) with lower moisture: the recycling coarse aggregates can not be adequately granulated; 2) with higher moisture: the cold-bonding recycling coarse aggregates don't have only sufficient durability (Mehta, 1986; Mindess & Young, 1981; Neville, 2000) but the redundant water also will be drained out during forming recycling aggregates (like consolidation in geotechnical engineering). The drained water will result in the excessively high water-to-cement ratio (w/c) or water-to-cementitious materials (w/cm) around the surface of the recycling aggregate. And the excessively high w/c or w/cm will immensely affect the strength, hardness, abrasion resistance, soundness, permeability of the cold-bonding recycling coarse aggregate (Mehta, 1986; Mindess & Young, 1981).

108 Sintering of Ceramics – New Emerging Techniques

(a) A commercial spirally-push machine (b) Photo of improper recycling aggregates

Finally the press ingot method (see Fig. 8) was developed and successfully granulated the cold-bonding recycling coarse aggregates. Fig. 8 also shows the procedure of press ingot

In the original designing concept of cement-based composites mixture proportions for producing the recycling coarse aggregates, the recycling resources were regarded as fillers (i.e aggregates of concrete). But the natures of recycling resources are quite different from primitive aggregates (e.g. particle shape, gradation, absorption, and so on). The purpose of exploring the optimum moisture of recycling resource for granulating aggregate is to avoid two issues: 1) with lower moisture: the recycling coarse aggregates can not be

(b) Photo of broken recycling aggregates

Fig. 6. Spirally push method.

(a) The water within cement-based composite was drained out

method and the procedure is described as follows:

Step 3: To press and form the recycling aggregates. Step 4: To take off the recycling aggregates from the mold.

Step 1: To fill the mixed cement-based composite into the mold.

Fig. 7. Immediately squeeze out method.

Step 2: To set up the pestle into the mold.

**4.2 Optimum moisture of granulation** 

(a) Step 1: To fill the mixed cement-based composite into the mold

(b) Step 2: To set up the pestle into the mold

(c) Step 3: To press and form the recycling aggregates

(d) Step 4: To take off the recycling aggregates from the mold

Fig. 8. The procedure of press ingot method.

Cold-Bonding Technique – A New Approach to Recycle

Innocuous Construction Residual Soil, Sludge, and Sediment as Coarse Aggregates 111

(a) Diameter = 24 mm (b) Diameter = 18 mm (c) Diameter = 12 mm

(d) Diameter = 8 mm (e) Diameter = 5 mm

(a) Diameter = 24 mm (b) Diameter = 18 mm (c) Diameter = 12 mm

Fig. 10. Photos of molds and recycling aggregates after improvement of particle shape.

Fig. 9. Photos of cold-bonding recycling coarse aggregates with various diameter.

The higher adopted stress is not always better for granulating cold-bonding recycling coarse aggregates. Because the water has the incompressible nature. While the too high stress is adopted for granulation, the water certainly will be drained out. Then the cold-bonding recycling coarse aggregate will generate cracks due to tensile stress in capillary pores caused by absorption of the drained water during unloading process. Therefore the proposed stress of granulation by using press ingot method is 35.0 to 42.0 MPa. The corresponding optimum moistures of recycling resources are shown in Table 8 and the blended cement-based composites contain the recycling resources with such moisture are shown in Fig. 2, Fig. 3, and Fig. 4. This result also implies that the cold-bonding technique is able to be applied to handle recycling resources with moisture and reduce the energy consumption and CO2 emission resulted from the oven-dry process. It is worth mentioning that the optimum moisture of blended recycling resource can be estimated by the proportion and optimum moisture of every constituent recycling resource. For example, a blended recycling resource is composed of 40 % B2-3 construction residual soil and 60 % lime sludge, its optimum moisture will be approximate 31 %.


Table 8. The optimum moistures of recycling resources.

#### **4.3 Improvement of particle shape**

The press ingot method was developed and successfully granulated the cement-based composites as cylindrical cold-bonding recycling coarse aggregates with five various diamemters of 24, 18, 12, 8, and 5 mm as shown in Fig.9. Mindess & Young (1981) and Mehta (1986) indicated that aggregate shap affects the workability of fresh concrete through their influence on cement paste requirments. The ideal aggregate particle is one that is close to spherical in shape. But the spherical shape is unfavorable for mechanical properties of concrete. Whereas both of the above contentions, the cylindrical cold-bonding recycling coarse aggregates were expected to be rounder (i.e. to smooth the four corners of cylinder). Only the molds of press ingot method with three various diamemters of 24, 18, and 12 mm was improved. Because the corner effects of cylindrical cold-bonding recycling coarse aggregate with diamemter of 8 or 5 mm are very limited. After improving particle shape, the molds and recycling coarse aggregates are shown in Fig 10.

The higher adopted stress is not always better for granulating cold-bonding recycling coarse aggregates. Because the water has the incompressible nature. While the too high stress is adopted for granulation, the water certainly will be drained out. Then the cold-bonding recycling coarse aggregate will generate cracks due to tensile stress in capillary pores caused by absorption of the drained water during unloading process. Therefore the proposed stress of granulation by using press ingot method is 35.0 to 42.0 MPa. The corresponding optimum moistures of recycling resources are shown in Table 8 and the blended cement-based composites contain the recycling resources with such moisture are shown in Fig. 2, Fig. 3, and Fig. 4. This result also implies that the cold-bonding technique is able to be applied to handle recycling resources with moisture and reduce the energy consumption and CO2 emission resulted from the oven-dry process. It is worth mentioning that the optimum moisture of blended recycling resource can be estimated by the proportion and optimum moisture of every constituent recycling resource. For example, a blended recycling resource is composed of 40 % B2-3 construction residual soil and 60 % lime sludge, its optimum

Type of recycling resource Optimum moisture

A granite sludge 19.5 % B granite sludge 20.0 % Lime sludge 45.0 %

The press ingot method was developed and successfully granulated the cement-based composites as cylindrical cold-bonding recycling coarse aggregates with five various diamemters of 24, 18, 12, 8, and 5 mm as shown in Fig.9. Mindess & Young (1981) and Mehta (1986) indicated that aggregate shap affects the workability of fresh concrete through their influence on cement paste requirments. The ideal aggregate particle is one that is close to spherical in shape. But the spherical shape is unfavorable for mechanical properties of concrete. Whereas both of the above contentions, the cylindrical cold-bonding recycling coarse aggregates were expected to be rounder (i.e. to smooth the four corners of cylinder). Only the molds of press ingot method with three various diamemters of 24, 18, and 12 mm was improved. Because the corner effects of cylindrical cold-bonding recycling coarse aggregate with diamemter of 8 or 5 mm are very limited. After improving particle shape, the

B2-3 construction residual soil 10.0 % B3 construction residual soil 14.0 % B4 construction residual soil 14.0 % B6 construction residual soil 14.0 %

moisture will be approximate 31 %.

Table 8. The optimum moistures of recycling resources.

molds and recycling coarse aggregates are shown in Fig 10.

**4.3 Improvement of particle shape** 

(d) Diameter = 8 mm (e) Diameter = 5 mm

Fig. 9. Photos of cold-bonding recycling coarse aggregates with various diameter.

Fig. 10. Photos of molds and recycling aggregates after improvement of particle shape.

Cold-Bonding Technique – A New Approach to Recycle

properties of cement-based composite will be.

significant advancement.

Clay lumps and friable particle

Chert (<2.4 sp gr SSD)

Mix No.

Criteria of

Innocuous Construction Residual Soil, Sludge, and Sediment as Coarse Aggregates 113

cold-bonding recycling coarse aggregate is lighter than primitive aggregate, and the optimum moisture of recycling resource for granulation directly influences the absorption of recycling aggregate. The more optimum moisture of recycling resource, the higher

Other characteristics of ASTM C33 (e.g. contents of chert, clay lumps and friable particles, materials less than 75 μm, and coal and lignite, abrasion, and soundness, etc.) of recycling coarse aggregate were conducted, too. The test results show that the other characteristics of recycling coarse aggregates satisfy the specification of ASTM C33 except the soundness of L-200 (see Table 10). The reason causing the soundness of L-200 is much higher than the ASTM C33 criterion of 12 % may be attributed to the fact that L-200 contains too calcium components to have adequate sulfate resistance (Mangat & Khatib, 1995). This result also implies that using lime sludge or other recycling resources with abundant calcium components to produce cold-bonding recycling coarse aggregates should choose the mixture proportions with cement amount lower than 200 kg/m3 to ensure their sulfate resistance. Table 11 shows the comparisons of properties of cold-bonding recycling coarse aggregate between before and after improvement of particle shape. The results indicate that the unit weight, voids, and abrasion of cold-bonding recycling coarse aggregate have the

Other characteristics of ASTM C33 (%)

Coal and

lignite Abrasion Soundness

Materials <75μm

B2-3-50 N.D. N.D. 0.45 N.D. 45.7 8.68 B2-3-100 N.D. N.D. 0.56 N.D. 40.7 4.93 B2-3-200 N.D. N.D. 0.42 N.D. 35.2 1.55 B3-50 N.D. N.D. 0.53 N.D. 48.9 11.16 B3-100 N.D. N.D. 0.49 N.D. 44.3 8.12 B3-200 N.D. N.D. 0.59 N.D. 39.2 4.62 B4-50 N.D. N.D. 0.33 N.D. 46.7 11.66 B4-100 N.D. N.D. 0.42 N.D. 42.8 8.47 B4-200 N.D. N.D. 0.44 N.D. 38.8 4.94 B6-50 N.D. N.D. 0.41 N.D. 43.8 8.23 B6-100 N.D. N.D. 0.41 N.D. 40.2 4.68 B6-200 N.D. N.D. 0.35 N.D. 34.5 1.47 L-50 N.D. N.D. 0.53 N.D. 38.8 7.65 L-100 N.D. N.D. 0.50 N.D. 37.4 9.87 L-200 N.D. N.D. 0.48 N.D. 37.8 81.47

ASTM C33 2.0 to 10.0 8.0 1.0 0.5 to 1.0 50.0 12.0

Table 10. ASTM C33 other characteristics of cold-bonding recycling coarse aggregates.
