CRUSHED WASTE CONCRETE IN STONE MASTIC ASPHALT MIXTURES

. Th e magnitude 7.6 Chi-Chi Taiwan in 1999 and the magnitude 7.9 Sichuan China in 2008 earthquakes caused many building damage and collapse, and a large amount of waste concrete caused many environmental problems. Th is study evaluates crushed waste concrete used as aggregate for stone mastic asphalt. On the basis of this study, the ANOVA of the permanent deformation test shows that the type of aggregate has a signifi cant eff ect at test temperature of 60 °C, but not signifi cantly aff ect at 25 °C. Th us, the ability of permanent deformation resistance of the crushed waste concrete mixture is better than that of 100% virgin crush stone mixture. Th e stability values of the crushed waste concrete mixtures are higher than the 100% crush stone mixture, especially in 50% crushed waste concrete plus 50% crush stone and coarse crush stone plus fi ne crushed waste concrete (C-crush stone plus F-crushed waste concrete). Th e stone mastic asphalt mixed with 50% crushed waste concrete plus 50% crush stone are more practicable for use than others.


Introduction
Due to 921 Chi-Chi Taiwan strong earthquake which caused many building damage and collapse in 1999, a large amount of waste concrete was demolished to the scrap heap and caused many environmental problems in this small island. In accordance with the statistical data report from the Ministry of the Interior, about 1 million cubic meters of waste concrete are produced every year in Taiwan. How to deal with the waste materials has become an environmental problem in a small island of Taiwan. Th e disposal of waste products primarily has three ways to deal with such as landfi lls, incineration and recycling. However, landfi lls are not suitable in Taiwan right now because of the large number of population living in such a small island so that there is no extra space for them. In addition, the waste building materials cannot be incinerated (Shen, Du 2004). Th us, one of the ways to reduce is crushed and recycled. Th e properties of the crushed waste concrete (CWC) have more impure materials, fracture and rough faces than general aggregates have (Shen, Du 2004, 2005. Stone mastic asphalt (SMA) concrete composed of crushed coarse and fi ne aggregate, mineral fi ller, asphalt cement, and stabilizing agent is designed to have higher contents of coarse aggregate (70-80% by weight), asphalt (over 6% by weight) and fi ller (8-13% by weight) than normal hot mix asphalt has (Radziszewski 2007;Roberts et al. 1996;Sivilevičius 2002;Vislavičius 2002). Specially, the high coarse aggregate contents in stone on stone contact produce highly resistance to rutting (Radziszewski 2007;Shen, Du 2005;Sivilevičius, Petkevičius 2002). Interlocking makes the aggregates diffi cult to displacement by compaction. Sand particles within the aggregate gradation, contacts disappear between stone particles, so interlocking of stone particles is weak (Haryanto, Takahashi 2007). Th e crushed waste concrete (CWC) used as aggregate in stone mastic asphalt (SMA) mixture can also provide more shear strength resistance than general asphalt mixtures do; and the probability of shear strains in asphalt concrete is higher when the pavement temperature is high (Laurinavičius, Čygas 2003). Th us, SMA with CWC increasing the stress resistance of asphalt concrete could solve the problem. In addition, the mixture is new and its engineering properties and performance need to be evaluated. Th us, in order to reduce waste concrete, an investigation of the CWC recycled as an aggregate and replaced all or part of the virgin aggregate for SMA mixtures was carried out.
Asphalt pavement in actual circumstances is subjected to the repetitive and changing transport load. As a result of the repetitive load impact, both elastic and plastic deformations occur to the pavement. Accumulation of plastic deformations in one or several layers leads to appearance of permanent deformations or rutting. Th is type of deformations reduces safety and convenience of traffi c (Haritonovs et al. 2010). Th e binder of modifi ed asphalt was used for the Marshall mix design; and permanent deformation and resilient modulus test were carried out.

Plan of study
Th e performance of laboratory compacted SMA mixtures were as follows: 100% virgin  crush stone (CS) (100% CS); 100% CWC;  50% coarse and fi ne CWC plus 50% coarse and fi ne  CS (50% CWC plus 50% CS); coarse CWC plus fi ne CS (C-CWC plus F-CS);  coarse CS plus fi ne CWC(C-CS plus F-CWC),  mixed with modifi ed asphalt cement. Permanent deformation and resilient modulus test were used for determining the laboratory performance of the CWC mixtures. Based on the laboratory tests, the ANOVA analysis was used to evaluate the signifi cant effects and to determine the best mix proportions based on laboratory performance.

Aggregate, binder and gradation
Th e CWC used as aggregate was obtained from Sindian City, Taiwan. CS was obtained from local quarry fi eld. Th e hydrated lime as a mineral fi ller was from a commercial source. Th e properties of CWC and CS aggregate are shown in Table 1. Processed CWC aggregate has higher angular, rougher surface texture, lower specifi c gravity, higher Los Angeles abrasion, higher sodium soundness, and higher water absorption than the CS.
Polymer modifi ed asphalt cement shown in Table 2 was from local petroleum company. Th e aggregate gradation used throughout the study shown in Table 3

Permanent deformation test
Ruts are treated as dangerous defects, since they might cause danger for traffi c, especially when the pavement is wet (Laurinavičius, Oginskas 2006). Th e permanent deformation test was performed employing the wheel-tracking device following the wheel tracking device testing procedure (Nienelt, Th amfald 1988). Th e facility was developed by the Swiss and modifi ed by the University of Hokkaido, Japan. Th e samples, mixed with optimum asphalt contents from Marshall mix design and fabricated by the rolling machine were 300×300 mm in section area and 50 mm in height. Th e test was performed using 2.18 MPa wheel load at test temperatures of 25±10 °C and 60±1 °C for dry condition. Th e depth of deformation was measured at 100, 200, 400, 800, 1400, 1890 and 2520 cycles. where M R -resilient modulus, MPa; P -applied load, kN; ν -Poisson's ratio; δ h -horizontal deformation, cm; hsample thickness, cm.

Results and discussion
Th e tests described above were conducted, and the data described in the following sections were collected on all samples.

Marshall design properties
Th e properties of the SMA mixture specimens are shown in Table 4. In Table 4 all of the stability values of CWC mixtures satisfi ed with the specifi cation requirements is greater than 6.24 kN and higher than that of 100% CS mixture. Compared to conventional CS mixtures in terms of the stability and fl ow values of all types of replacement, the max value of stability and min fl ow occur in the 100% CWC and C-CS plus F-CWC mixture, respectively. All of the voids in mineral aggregate (VMA) greater than 17% are satisfi ed with the criteria. However, 100% CWC and C-CWC plus F-CS are not satisfi ed with fl ow criteria of the Marshall mix design. As shown in Table 1, the bulk specifi c gravity of CWC is less than that of CS. Th is is primary reason that unit weights of all SMA with CWC are less than CS. In addition, CWC aggregate has more angular and rougher surface texture than CS has. Th us, SMA with CWC has higher OAC and higher stability due to increase resistance by aggregate's stone on stone contact (interlocking).

Permanent deformation
Th e results of the average deformation of each sample from the tests at 25 and 60 °C are plotted in Figs 1 and 2, respectively. All of the deformations are less than 1.00 mm at 25 °C and 2.50 mm at 60 °C, and the CS has the lowest deformation at test temperature of 25 °C, but the highest deformation at test temperature of 60 °C. In Fig. 2, the 100% CWC and 50% CWC plus 50% CS have the lowest deformation. Th e deformation at 60 °C indicates that it appears to be plastic fl ow not densifi cation. Due to the internal friction between aggregate particles providing the ability of deformation resistance, plastic fl ow can be minimized by using large size aggregate, angular and rough textured coarse and fi ne aggregates (Roberts et al. 1996). Th erefore, the smaller observed deformation of the 50% CWC plus 50% CS suggests that these mixes have more angular and rougher particles than that of CS mixture, and thus have higher internal friction. In general, it is believed that the higher asphalt contents provide higher plastic fl ow susceptibility. Th e high plastic susceptibility may lead to high permanent deformation, due to too much asphalt cement in the mix causing loss of internal friction between aggregate particles, which results in the loads being carried by the asphalt cement rather than the aggregate structure. In Table 4, although the CWC mixtures have higher asphalt contents than the CS mixtures, this is not the case for deformation following the preceding description. Th e phenomenon may be explained by the fact that the high proportion of internal friction plays the main role in deformation resistance. To determine the statistical signifi cance of the eff ect of aggregate type on the wheel load deformation test, a one-way analysis of variance (ANOVA) was performed on the test. Th e ANOVA was performed to determine whether the treatments were signifi cant at a confi dence limit of 95%. Table 5 shows the results of the ANOVA test and indicates that the type of aggregate has a signifi cant eff ect at temperature of 60 °C, but not a signifi cant eff ect at temperature of 25 °C. Th is situation suggests that the angular and rough textured aggregate play the main role in the deformation resistance of SMA at high temperature.

Resilient modulus
Th e M R test results are shown in Fig. 3. As can be seen in Fig. 3 (Roberts et al. 1996). Fortunately, low temperature cracking never happens in Taiwan due to the high and mild temperatures present the whole year. Th us, the high M R values of the CWC mixtures provide a good capacity for distress resistance.

Conclusions
Th e data analysis indicates that the performance of SMA with CWC in Taiwan is related to the highly crushed face and high absorption of asphalt cement aggregate. Th e aggregate contributed to the internal friction for deformation resistance. Based on the results of this study, the following conclusions and recommendations are suggested to improve the performance of SMA with CWC: the stability values of the CWC mixtures are higher  than the 100% CS mixture, especially in 50% CWC + 50% CS and C-CS + F-CWC; the ANOVA of the permanent deformation test  shows that the type of aggregate has a signifi cant effect at temperature of 60 °C but not at temperature of 25 °C. Th us, the ability of permanent deformation resistance of the CWC mixture is better than that of 100% CS mixture; the SMA mixed with 50% CWC + 50% CS are more  practicable for use than others; Fig. 3. Resilient modulus test results the CWC used as aggregate in SMA mixture can  provide better performance than general asphalt mixtures do, and fi nd a way to solve the environment problem related to the large amount of waste concrete.

Acknowledge
Th is study was supported by National Science Council of Taiwan (NSC 89-2211-E011-071).