br Conclusions The s s of Pb and
Conclusions The s/s of Pb and Cu contaminated slurry using cement and rice husk ash (RHA) was investigated. This study investigated the potential of replacing 20%–40% of the cement used for the s/s of Cu and Pb with RHA. It was observed that an increase in the binder content from 100 kg/m3 – 300 kg/m3 was effective for the immobilisation of Pb in the stabilised slurry through the reduction of the apparent SR 95531 hydrobromide coefficient (i.e. reduced from to 2.13 × 10−14 m2/s to 2.54 × 10-19). However, a minimum binder content of 200 kg/m3 was also sufficient to attain a diffusion coefficient of Cu as low as 2.1 × 10-18 m2/s at RHA content of 40%. The reduction of the required cement for s/s by 40% and then replaced with a cheaper agricultural waste product RHA will save several developing countries many dollars in rehabilitation of contaminated sites. The LX determined for all the samples was very high (above 9) giving an indication that treatment was very effective. The main leaching mechanism controlling the immobilisation from the waste form was diffusion and long-term kinetically controlled dissolution. The long-term kinetically controlled dissolution processes are predominately precipitation and sorption. Aside these two processes, physical encapsulation was also very important physical mechanism which helped in the immobilisation of Cu and Pb. In addition, the microscopic study using the MIP and the XRD test showed that the incorporation of the RHA initiated changes in the stabilised waste form. However, other microscopic study such as the use of scanning electron microscope (SEM) could also be employed for further studies. The pH controlled leaching as simulated by the batch leaching experiment also showed that the leaching of both Cu and Pb were pH sensitive. The amount of binder content was however important for the immobilisation of Cu and Pb under changing pH conditions. It should be noted that the incorporation of RHA could lead to order of magnitude increase in the leachability of Cu under near neutral pH.
Acknowledgements This study is sponsored by the Natural Science Foundation of China (grant no. 51178161), 111 Project (grant no. B13024) and the Fundamental Research Funds for the Central Universities (grant no. 2017B00914)
Introduction Highway and pavement engineers are facing concrete pavement damages nowadays due to alkali-aggregate reaction (AAR). AAR is detrimental when it causes significant volume expansion of concrete and results in cracking. There are two types of alkali-aggregate reaction, which are the alkali-silica reaction and alkali-carbonate reaction. The most prevalent form of AAR is the alkali-silica reaction (ASR). An ASR phenomenon is a chemical reaction between the alkali hydroxide coming from hydraulic cement and silica content from aggregate used in concrete. A gel is formed during this chemical reaction, namely ASR gel . When moisture comes in contact with this gel, it swells in volume and exerts pressure in concrete , . It leads to the formation of microfractures in concrete, which results in spalling and cracking .