Concrete is a common and the most critical material used in construction. Increasing the usage of concrete and the need for cement manufacturing, and the vital role of environmental matters and particular emphasize on sustainability of improvement have led into requirement for reviewing production of cement to become clear (H. A. Abdel-Gawwad, Mohammed, & Alomayri, 2019). Employing industrial side products as the binder is a good example of possible selection instead of the Ordinary Portland cement. This cementitious material has low environmental impact, and better performance such as high mechanical properties (Behfarnia & Rostami, 2017; R. J. Thomas, Gebregziabiher, Giffin, & Peethamparan, 2018), high acid resistance (Sturm, Gluth, Jäger, Brouwers, & Kühne, 2018; Temuujin, Minjigmaa, Lee, Chen-Tan, & van Riessen, 2011), fire (H. Y. Zhang, Kodur, Qi, Cao, & Wu, 2014), freeze and thaw (Shahrajabian & Behfarnia, 2018) and abrasion (Mohebi, Behfarnia, & Shojaei, 2015) than Ordinary Portland cement, thereby being able to be used as a part or 100 substituted material with cement in preparing concrete and evolving as the most reassuring cementitious material taking the place of cement (Cheng et al., 2018). The employment of binders which are alkali-activated on the basis of materials high in calcium, has received a lot of attention, by bringing into play the granulated ground blast furnace slag and other industrial by-products (Pacheco-Torgal, Labrincha, Leonelli, Palomo, & Chindaprasit, 2014). Conventional (two-part) alkali-activated binders are constructed by a reaction happened between a solution of alkali hydroxide, silicate, carbonate, or sulfate which is aqueously concentrated for example, and solid aluminosilicate precursor which is two parts supplying to water (Duxson, Fernández-Jiménez, et al., 2007; Provis, 2009, 2014; Provis & Van Deventer, 2013). Nevertheless, there are some impracticalities associated with dealing with the huge quantities of viscous, corrosive, and perilous alkali-activator solutions have applied a lot of pressure to the development of one-part alkali-activated binders. That could be used similarly to ordinary Portland cement (Luukkonen, Abdollahnejad, Yliniemi, Kinnunen, & Illikainen, 2018). To solve the problems caused by two-part alkali-activated binders, one-part alkali-activated binders were prepared by mixing a precursor of solid aluminosilicate, a solid alkaline material, and practicable additives in composition to water. However CO2 emission is possible to be reduced by 25–50% (Duxson, Provis, Lukey, & van Deventer, 2007; Robert J Thomas, Ye, Radlinska, & Peethamparan, 2016), using materials which are alkali-activated, but they have not gained consideration from the industry as a result of the long-term properties they perform, especially drying shrinkage. The most crucial reason which narrows the extended application of this material is the micro –cracks which root in drying shrinkage (Melo Neto, Cincotto, & Repette, 2008; Ye & Radlińska, 2016). The drying shrinkage of alkali-activated concrete is under the influence of raw materials reaction, dose and type of chemical activator and condition of curing (Melo Neto et al., 2008).
It is illustrated by Collins and Sanjayan that the drying shrinkage of alkali-activated slag is approximately three times bigger than it is in OPC concrete provided for specimens which are cured at the surrounding temperature of 23 ºC and the relative humidity of 50% (Collins & Sanjayan, 2000). The chemical features of the activator is able to have a determinant impact on the shrinkage of alkali-activated slag. Behfrnia and Rostami shown the direct relationship between the properties of alkali-activated slag concrete and the ratio of alkali to slag (Behfarnia & Rostami, 2018). Taghvaei et al. investigated the influences of sodium silicate modulus and concentration of alkali on the properties of alkali-activated slag concrete. They reported an optimum concentration of 5.5% and a silicate modulus of 0.85 in order to avoid rapid setting time, reduced high drying shrinkage and compressive strength (Taghvayi, Behfarnia, & Khalili, 2018). Neto et al. carried out a study on how different activators affect drying and autogenous shrinkages of AAS in a way in which a silica modulus of 1.7 (SiO2/ Na2O) had activated the slag binders and the slag mass was 2.5, 3.5 and 4.5% Na2O. The results showed an increase in the total shrinkage ( drying and autogenous) by increasing the amount of SiO2 and Na2O in a manner in which the drying shrinkage was considerable in comparison with the autogenous shrinkage (Melo Neto et al., 2008). In addition to activator, drying shrinkage and the properties of the alkali-activated slag concrete are also affected by the curing conditions including temperature and relative humidity (Komljenović, Baščarević, & Bradić, 2010; Pacheco-Torgal et al., 2014). Mohebi et al. mentioned that compressive strength was increased with temperature curing. The kinetic energy was increased by heat curing and also the development of strength was accelerated. Also, at high temperatures (60–95 ºC) the development rate of compressive strength was lessened (Mohebi et al., 2015). The time of temperature curing has a great effect on strength. Too much time of temperature curing can reduce performance of alkali-activated concrete (Singh, Ishwarya, Gupta, & Bhattacharyya, 2015). The results of Kumarawal's experiments shows that the compressive strength of the specimens cured in oven is higher than environmental curing and the optimum compressive strength was obtained at 60 ° C (Kumaravel, 2014).
Table 1
The chemical composition of the materials (%)
Material | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | SO3 | K2O | Na2O | L.O.I |
Slag | 36.50 | 11.00 | 1.00 | 38.50 | 7.80 | 0.30 | 0.80 | 0.65 | n.a. |
Cement | 32.50 | 5.80 | 3.10 | 60.00 | 3.10 | 2.00 | n.a. | n.a. | 1.10 |
Table 2
The chemical composition of the sodium metasilicate.5H2O (%)
SiO2 | Na2O | H2O |
29.50 ± 0.2 | 29.50 ± 0.2 | 41 |
Table 3
properties of lightweight fine aggregate
Apparent density (kg/m3) | Bulk density (kg/m3) | Water absorption (%) | Fineness modulus |
1400 | 800 | 10 | 2.45 |
Table 4
properties of lightweight coarse aggregate
Apparent density (kg/m3) | Bulk density (kg/m3) | Water absorption (%) | Diameter (mm) |
1300 | 700 | 8 | < 12.5 |
Table 5
Mix | Slag (kg/m3) | Sodium metasilicate (kg/m3) | Added water (kg/m3) | Fine Aggregate | Coarse aggregate | Type of curing |
LAF | NAF | LAC | NAC |
A1 | 400 | 72 | 156.32 | 498.94 | - | 308.8 | - | Water |
A2 | 475 | 85.5 | 185.6 | 439.7 | - | 272.2 | - | Water |
A3 | 400 | 80 | 155 | 492.9 | - | 305.2 | - | Water |
A4 | 400 | 72 | 156.32 | 498.94 | - | 308.8 | - | Plastic cover |
A5 | 475 | 95 | 184.1 | 432.6 | - | 267.8 | - | Water |
A6 | 475 | 95 | 184.1 | 432.6 | - | - | 545.9 | Water |
A7 | 475 | 95 | 184.1 | - | 834.4 | - | 545.9 | Water |
OPC | C = 442.48, w/c = 0.42 | 185.84 | 484.6 | - | 323.1 | - | Water |
Findings show that drying shrinkage of alkali-activated slags can be reduced by heat curing. It can be due to the limited unbound water consumption during chemical reactions. Unbound water lose over time can result in notable drying shrinkage strains for alkali-activated binders that cured at ambient temperature, particularly within the first two weeks (Chi & Huang, 2013; Wallah & Rangan, 2006). Zijian et al. investigated the effect of relative humidity on the shrinkage by using expanders. The results showed that the shrinkage in the alkali-activated slag mortar is linearly correlated with the relative humidity (Jia, Yang, Yang, Zhang, & Sun, 2018) and in addition, the time of curing, the difference between ambient temperature and concrete, effect on the rate of evaporation water from the concrete surface and consequently the shrinkage (Hasanain, Khallaf, & Mahmood, 1989). However, drying shrinkage is dependent on binder, the amount and type of aggregate is affected in limiting the drying shrinkage. Light weight composites have extent absorbency and before being mixed are prewetted to make sure there is no water lose from the mixture. After the concrete is set, the stores water in the composites releases gradually, this makes cementitious materials able to keep hydration after the termination of the external curing, as long as the composites contain water. The difference between the additional water absorbed in aggregates influences the amplitude of drying shrinkage in concrete with light weight or normal weight during the stage of hardening in which significant changes take place in the properties of the concrete over time, especially in comparatively first stages. As the light weight coarse composites absorbency is significantly higher than in composites with normal weight, the result of water excess is reducing the light weight concrete during shrinkage (Jiajun, Shuguang, Fazhou, Yufei, & Zhichao, 2006). Meg and Khayat’s findings illustrate that using light weight sand in UHPC containing 4% silica fume, 34% class C fly ash with 0.2 w/b is able to decrease the relative humidity and autogenous shrinkage considerably. Absence of light weight sand and presence of 75% light weight sand showed relative humidity of roughly 83% and 93%, respectively at 7 days. Before being mixed and used for internal curing, light weight aggregate is a good candidate to be saturated for the aim of water accumulation (Meng & Khayat, 2017). Then the accumulated water release in the period of hydration of binders into the system in order to make up for the loss of moisture and decrease shrinkage. Existing studies have shown different results on the shrinkage of lightweight aggregate. Light-weight concrete in comparison with normal weight aggregate concrete showed smaller shrinkage in ref (Fujiwara, 2008; LIN, 2004; Lura, Van Breugel, & Maruyama, 2002), while in contrast the shrinkage in ref (Al-Attar, 2008; Asamoto, Ishida, & Maekawa, 2008; M. H. Zhang, Li, & Paramasivam, 2005) was more. The reason can be the variety of moisture load corresponding light-weight concrete drying shrinkage during the time differing highly with those of normal weight concrete, especially in the stage of hardening (Fujiwara, 2008). In this research the effect of slag content in one-part lightweight alkali-activated slag concrete (OLWAAS) mixture that activated with sodium metasilicate with weight ratio of 18% and 20% of slag and two curing methods, such as water curing and plastic cover curing on the slump, setting time, compressive strength and drying shrinkage were studied and examined. To investigation the effect of lightweight aggregate on properties and drying shrinkage of OLWAAS, replacement fine aggregate, coarse and both with Leca as lightweight aggregate, respectively.