The particle-size effect of waste clay brick powder on its pozzolanic activity and properties of blended cement

https://doi.org/10.1016/j.jclepro.2019.118521Get rights and content

Highlights

  • Pozzolanic activity of waste clay brick was enhanced by mechanical grinding.

  • CBP with smaller particle size could accelerate the early-age hydration.

  • Paste containing CBP with smaller size showed better performance at later ages.

  • Environmental impact and cost of CBP manufacture were quantitatively calculated.

Abstract

The manufacture of cement is considered as a high energy consumption and environmental pollution process, and it is necessary to figure out a way to reduce the consumption of cement in construction industry. The waste clay brick is a kind of construction waste with pozzolanic activity, which could be used to prepare blended cement after grinding. However, the particle size of clay brick powder (CBP) will influence its pozzolanic activity and properties of blended cement, which needs to be clarified. Therefore, in this study, the pozzolanic activity of CBP and properties of blended cement containing CBP were investigated. The results show that with the increase of grinding time, the CBP particles tend to be refined and spherical, which will increase the specific surface area and pozzolanic activity of CBP. The decrease of CBP particle size in blended cement paste can accelerate the early-age hydration and decrease the setting time since the ultrafine CBP could become the crystallization nucleus. The compressive strength of mortars with 30% CBP is 10%–35% lower than that without CBP, and the smaller the CBP particle size, the faster the compressive strength grows. Moreover, the hydration products and pore structure results also prove that the CBP with smaller particle size will consume more calcium hydroxide to react, which could make the microstructure denser and obtain stronger compressive strength growth at later ages. Meanwhile, the environmental impact and cost calculations indicate that the energy intensity and CO2 emissions of blended cement are obviously lower than Portland cement. It could be concluded that the pozzolanic activity of CBP will be enhanced with the decrease of particle size, and this research provided the reference for application of waste clay brick to produce green construction materials.

Introduction

Nowadays, cement is widely used all over the world. Over 4 billion tons of cement were manufactured in 2017, and China has accounts for about half of the total amount (Song et al., 2019). The manufacture of cement is considered as a high energy consumption and environmental pollution process (Fort et al., 2018). According to studies (Ali et al., 2011, Allwood et al., 2010), the cement industry should take the responsible for 12–15% of total energy consumption in industry and approximately 6–8% of global carbon dioxide emission. Therefore, its crucial to find out some eco-type cementitious materials to replace or partially replace cement to reduce the energy consumption and CO2 emission.

The rapid urbanization in China makes a large amount of construction demolished, which far exceeds the current disposal capacity of construction wastes. Massive construction wastes are just buried in landfills, occupying the precious land resources and polluting the environment. (Ge et al., 2015, Zhao et al., 2018). In those construction wastes, the waste clay bricks (WCB) could account for over 50% according to statistics (Cheng, 2016). The clay brick is exposed to 500–900 °C during the manufacture process, which could make the transformation of silicate crystal structure into amorphous compounds (Pacheco-Torgal and Jalali, 2010, Aliabdo et al., 2014, Schackow et al., 2015). Those amorphous compounds could react with alkali from the cement hydration or alkali-activator to form the binding products, which will take a beneficial effect on the development of mortar and concrete properties (Zawrah et al., 2016, Tuyan et al., 2018, Shao et al., 2019). Therefore, the ground WCB have the potential to be used as eco-type cementitious materials, which could gain the environment benefits by increasing construction waste consumption and reducing CO2 emission by cement industries (Naceri and Hamina, 2009, Kaminskas et al., 2006, Robayo-Salazar et al., 2017).

The influence of adding clay brick powder (CBP) in mortars or concretes has been studied (Katzer, 2013, Lavat et al., 2009, Ge et al., 2012, Kulovaná et al., 2016) and the results indicate that when the CBP replacement ratio is no more than 30%, the properties of mortars or concretes are almost similar to the reference samples containing no CBP. For long curing age, the mechanical properties of samples with CBP could get further improved, and the hydration products contained CSH, CAH and CASH could be generated by the pozzolanic reaction of CBP with cement hydration production Ca(OH)2 (Li et al., 2016, Lin et al., 2010, Ortega et al., 2018). The pozzolanic activity of pozzolans could be affected by their particle size. It is reported that the fly ash with particle size below 20 μm has a higher pozzolanic activity compared with the fly ash having particle size from 75 to 150 μm (Ranganath et al., 1998), and this conclusion also could apply to the CBP. A study (Zheng et al., 2011) has been conducted on the mortar containing CBP graded by 4 particle sizes (40 μm, 60 μm, 100 μm and 300 μm), the result reveals that the sample with 60 μm size CBP has a higher strength compared with other samples. However, the CBP is still not fine enough to obtain obvious pozzolanic activity, and the main role of CBP in this experiment is the micro-aggregate effect.

Therefore, in this study, the CBP was activated by mechanical grinding, and four kinds of CBPs with different particle sizes (the medium diameters are 27.1 μm, 15.8 μm, 10.5 μm and 3.4 μm) were obtained by grinding different times. According to previous study (Shao et al., 2019), blended cement containing 30% CBP was chosen to prepare paste and mortars in this study. The evolution of microstructure and surface binding energy of CBP by grinding was analyzed by the method of scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The workability and setting time, the hydration heat, compressive strength, hydration products and pore structures of pastes or mortars were tested to investigate the particle-size effect of CBP on the properties of blended cement. To evaluate the environmental impact of blended cement, the material sustainability indicators (MSIs) and cost of blended cement were calculated in this study. This study can provide the reference for application of waste clay brick to produce green construction materials.

Section snippets

Materials

The CBP was obtained by grinding waste clay bricks, which were collected from a demolition site around Nanjing. These waste clay bricks were crushed and sieved to obtain coarse particles, and then put into a ball mill to grind with different times. After the early exploration of grinding technique, the grinding times were set as 10min, 30min, 60min and 120min with 400 revolutions per minute. Finally, four kinds of CBPs with distinct particle size difference were selected. The four kinds of CBPs

Microstructure of CBP

Fig. 3 illustrates the SEM images of CBPs with different particle sizes. From Fig. 3(a)∼(d), the particle size of CBP is gradually refined and the edges and corners of CBP particles also are gradually ground off with the increase of grinding time. Especially in Fig. 3(f), the CBPs are no longer irregular particles, the shape of CBP tends to be spherical. The refinement and spheroidizing effect could make the specific surface area of CBP increased, which will increase the contact area of the

Conclusions

In this study, the waste clay bricks were ground into powders with four different particle sizes, and then those CBPs were used to replace 30% cement to prepare pastes or mortars. The pozzolanic activity of CBPs with different particle sizes were analyzed, and then workability, setting time, hydration heat, compressive strength, hydration products and pore structures of pastes or mortars were tested to evaluate the particle-size effect of CBP on properties of blended cement. Finally, the MSIs

Acknowledgements

This work was supported by National Natural Science Foundation of China (No. 51578141), National Program on Key Basic Research Project (973 Program) (No. 2015CB655102) and China-Japanese Research Cooperative Program-Ministry of Science and technology in China (2016YFE0118200).

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