Iron ore tailings (IOTs) are gradually used as building materials to solve the severe ecological and environmental problems caused by their massive accumulation. However, the bulk density of IOT as aggregate is too large, which seriously affects the concrete properties. Therefore, in this paper, the effect of hydroxypropyl methylcellulose (HPMC) on the workability, mechanical properties, and durability of concrete prepared from IOT recycled aggregate was studied. The action mechanism of HPMC on the workability and the mechanical properties of the IOT concrete was analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). The results show that HPMC can effectively improve the segregation problem caused by the sinking and air entrainment of IOT aggregate and improve the crack resistance of concrete with little effect on its compressive strength and electric flux. These results are due to the air-entraining thickening effect of HPMC, which improves the slurry viscosity, hinders the sinking of aggregate, and improves the workability. At the same time, HPMC film, after concrete hardening, will bridge the slurry and aggregate through physical and chemical effects, hinder the propagation of microcracks, and improve the crack resistance.
With the continuous development of the global social economy, the consumption of concrete as a building material is increasing rapidly at the rate of 4.4 billion tons per year [1]. More than 75% of concrete raw materials are composed of aggregates [2]. The acquisition of natural aggregates has a serious impact on the ecological environment. As a developing country, the vigorous development of infrastructure has promoted China&#;s rapid development. The overuse of land, minerals, water, and other non-renewable precious natural resources in the short term will damage the survival of our future generations. Currently, mineral admixtures such as fly ash (FA) [3], silica fume [4], coal bottom ash [5], and ground granulated blast furnace slag (GGBFS) [6] have been used as partial replacement of cement in concrete, which not only cuts carbon emission footprints but also reduces costs of production. Therefore, an eco-friendly production mode must be adopted to realize the sustainable development of the concrete industry.
Iron has always played an essential role in the development of modern human civilization [7]. After the iron is extracted from the iron ore by various beneficiation processes in the concentrator, a large number of iron tailings are discharged to the IOT pond for stacking [8]. China&#;s cumulative stockpile of tailings reached 60 billion tons, including 475 million tons of IOTs based on the &#; Chinese development report. IOTs have become one of the most critical solid wastes in the world [9]. Their massive accumulation will not only cause land pollution, poor water quality, and aggravation of dust but also threaten human health [10]. The managers of mining enterprises need to spend more resources to maintain IOT ponds every year [11]. More seriously, the existence of tailing dams is a potential safety hazard, and the human life safety events caused by the tailings dam breaks around the world are increasing every year [9]. With extensive research on the recycling of IOT, the recycled IOT is classified into four categories at home and abroad: (i) extracting valuable metals in IOT [12]; (ii) used for a backfill material [13]; (iii) turned into a building material [14,15]; (iv) reclaiming farmland on the tailings dumping ground. The large-scale application of iron tailings in concrete building materials has become the focus of all major sectors of society.
Compared with the natural aggregate, the IOT aggregate in concrete is made from the waste stone stripped from the open-pit mine through crushing and screening [16]. The IOT coarse aggregate has many edges and corners [17]. At the same time, the IOT fine aggregate has many powders during the crushing, which further increases the IOT specific surface area, increases the water demand, and leads to poor workability of IOT concrete [18].
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Cellulose ethers (CEs) have been widely used in modern building products due to the function of preventing uncontrolled water loss into porous matrix [19]. HPMC, a type of CH, has been used because of its better effect on improving the workability of concrete [20]. The water retention of HPMC mainly hinders the migration of water molecules between pores through the action of internal groups. Pourchez et al. reported that CE slows down the hydration process of cement, which helps to reduce the loss of water [21]. Brumaud et al. revealed how CE slows down the cement hydration process [22]. Weyer et al. showed that it is necessary to control the CE content [23]. Only adding an appropriate amount of CE can slow down the hydration of cement.
Until now, researchers have studied the mechanism of different kinds of CEs in paste and mortar, but there are few reports of HPMC on concrete, especially the concrete used by IOTs as an aggregate. This paper focuses on the effect of HPMC on the workability of full IOT aggregate concrete. Moreover, the influence mechanism of HPMC on the mechanical properties of IOT concrete was also clarified.
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