Study on freeze-thaw resistance with NaCl of desert sand engineering cement composites
Introduction
Engineering cement composite (ECC) is a high-performance concrete with high durability, high sustainability, typical moderate tensile strength and a higher ductility are 4–6 MPa and 3–5% (300–500 times that of concrete) (Li, 2003; Ma et al., 2015). Examples of applications of ECC in transportation, building, and water infrastructures can be found in reference (Li, 2003, 2019; Li et al., 1993; Zhang et al., 2017). ECC is a mixture that contains of cement, water, fly ash, fine sand, randomly distributed ultrafine microfiber and chemical additive. The type, size and amount of fiber and matrix ingredients, along with interface characteristics are tailored for multiple cracking and controlled crack width (Li and Leung, 1992). Through the micro-mechanism analysis of ECC, we found that the performance of ECC material is more severely affected by the content and size of the fine aggregate, and that the high-content and large-size of fine aggregate can increase the fracture toughness of the matrix while reducing the interface friction (Sahmaran et al., 2009; Li et al., 1995). Therefore, fine aggregate type and grain size seriously affect the achievement of target ductility. To achieve the target ductility, most of the reported that expensive microsilica sand which have the feature of maximum particle size of 200 μm have used in polyvinyl alcohol engineered cementitious composite (PVA-ECC) (Li et al., 2001).
In order to reduce the cost of ECC, the method of replacing microsilica sand with coarser river sand is considered by some scholars (Sahmaran et al., 2009; Deng et al., 2018; Guan et al., 2019). Due to the shortage of river sand resources and the long distance transportation to increase the project cost, people in recent years had to turn their attention more to desert sand. Desert sand has a small particle size and a smooth round surface. It is distributed throughout the world, such as Arabia and Australia. And it is also widely distributed in northwest China, such as Ningxia Hui Autonomous Region, Xinjiang Uygur Autonomous Region and Qinghai Province. Among them, Ningxia is surrounded by the Tengger Desert and the Mu Us Desert (respectively shown in Fig. 1 (a) (b), and the desert sand resources are quite rich. If fully utilizing local desert sand materials, it is possible to effectively reduce cost and the CO2 emissions that are generated during the transport process. Therefore, considering availability, environmental sustainability and economicreasons, it is better to use local ingredients, namely desert sand, when ECC is more widely adopted inlarge-scale applications.
By considering availability, environmental sustainability and economic reasons, some scholars have proposed to use sand collected from the Desert (named desert sand or dune sand) to prepare concrete materials (Ren et al., 2018; Guettala and Mezghiche, 2011; Wang et al., 2014; Yan et al., 2019; Zhang et al., 2019; Liu et al., 2016),and found it is feasible. But some scholars (Bouziani, 2013; Seif, 2013) also found as the amount of desert sand increasing, the compressive strength of concrete gradually decreases. Then, so some scholars have been considered to apply desert sand to ECC materials. Meng Dan et al. (Meng et al., 2017) using local dune sand to developed a PVA-ECC. This material is compareble to the reinforced concrete structures, because it not only has the characteristics of low tensile strain capacity, but also the cost is low. M. Iqbal Khan et al. (2017) collected local white and red dune sands that from the Arabian Desert, and investigated the effects of mix design on the tensile ductility of ECC. The conclusion is that the dune sand-based ECC mixture can provide comparable results to the silica sand-based ECC mixture. Our group's study on ECC (Che et al., 2017, 2019) made with desert sand from China's Mu Us desert. The test results show that it is possible to use undisturbed desert sand instead of silica sand to make high-ductility fiber reinforced concrete. To distinguish it from traditional ECC materials using silica sand, we named it DSECC. Existing studies have shown that the mechanical properties of DSECC materials suffice engineering requirements.
In the surrounding areas of the desert, the amount of evaporation is much larger than the number of precipitation. The water contains a large amount of salt ions (mainly chloride), and the temperature difference in Ningxia, is large, especially in the winter. It has been found that the freeze-thaw resistance is the most important factor leading to structural degradation and even damage (Qiu et al., 2020). Scholars have carried out a series of studies on the antifreeze performance of ECC. As a result of these investigations, it has been shown that the standard ECC mixture is highly durable under freeze-thaw cycles (FTC) with/without de-icing salts (Şahmaran and Li, 2007; Li et al., 2003; Sahmaran et al., 2012; Nam et al., 2016; Yun and Rokugo, 2012; Wang et al., 2017). The result found that the ECC mixtures using microsilica sand with a large amount of fly ash remains durable; the presence of micro PVA fibers can resulting pressure releasing effects under freeze-thaw conditions, thus it is considered effective for frost resistance.
To complete a part knowledge of ECC using desert sand (DSECC), the freeze-thaw resistance with NaCl of DSECC was mainly investigated in this paper. To study the durability of DSECC apply to the structures in dry and wet alternation and salt solution, such as dams, sluices, lining channels, etc., the single side salt freezing test and compression test after freezing and thawing were used. The appearance, water absorption rate, mass loss rate, relative dynamic elastic modulus, longitudinal ultrasonic speed and compressive strength of the DSECC using two types of desert sand were studied.
Section snippets
Materials
Locally, the grade is P. O 42.5 Ordinary Portland Cement, fly ash Ⅰ, polyvinyl alcohol fiber (PVA fiber) made in China, freshwater and two desert sands were the main ingredients of preparating the DSECC. PVA fiber's properties are shown in Table 1. In this experiment, it can be observed that PVA fiber with a length of 12 mm and a diameter of 39 μm. Two types of desert sands were collected from the Tengger Desert and Mu Us Desert in China, denoted T and M, respectively. Both T and M were sieved
Appearance
The obvious characteristic of freeze-thaw damage of ECC specimens is the generation of microcracks inside the specimen and the spalling of the outer surface. Among them, the peeling of the outer surface can reflect the degree of freeze-thaw damage to a certain extent.
Fig. 6 is a diagram showing the appearance of DSECC after different FTC. It can be seen that as the number of FTC increasing, the degree of external peeling damage of DSECC gradually increases. Before the freeze-thaw cycle 8 times,
Conclusion
In this paper, by comparing the freeze-thaw resistance with NaCl of T-DSECC and M-DSECC, the following conclusions can be drawn:
- 1)
Freeze-thaw cycles can accelerate the damage of the appearance. Before the freeze-thaw cycles 8 times, there was no obvious peeling, but slight cracks were visible to the naked eye; after 16 cycles of freezing and thawing, the cracks deepened and has slight peeling.
- 2)
As the number of freeze-thaw cycles increasing, the water absorption rate, the mass loss rate and the
CRediT author statement
X An: test, Data curation. J L Che: Conceptualization, Writing – original draft, Writing – review & editing. H F Liu: Data curation. S Y Yang: Visualization. S I Doh: Formal analysis
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the Ningxia Natural Science Foundation of China(Grant No. 2020AAC03041) and in part by the National Natural Science Foundation of China (Grant No. 52068060 and 51868065).
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