Mechanical and Durability Study of Steel Fiber-Reinforced Geopolymer Concrete

Abstract

The global use of concrete is second only to water. As the demand for concrete as a construction material increases, so also the demand for Portland cement. It is estimated that the production of cement has increased from about from 1.5 billion tons in 1995 to 2.2 billion tons in 2010. So it is inevitable to find an alternative material to the Portland cement whose manufacturing process is most resource consuming. The utilization of supplementary cementing materials such as fly ash, silica fume, granulated blast furnace slag, rice-husk ash has encouraged the researchers to develop alternative binder paste to completely replace cement paste. Geo polymer concrete is an innovative construction material which shall be produced by chemical action of these inorganic amorphous binders. In this we make use of supplementary cementitious materials which react with alkaline activators to form Al-O-Si-O gel which has similar bonding strength as C-S-H gel. Geopolymer concrete itself is very brittle so to increase its flexural and tensile strength Fibers have been incorporated. In this work durability study was performed on the geopolymer concrete with steel Fibers by curing them in harsh chemical environment, it was observed that there was slight reduction in density and compressive strength of GPC exposed to the chemical solutions like HCl and H₂SO₄ than concrete in ambient condition, which was only about 1.4% and 0.76% respectively. These results indicate that the geo polymer concrete has shown better performance under harsh environment when compared to normal concrete.

1 Introduction

Cement Concrete (CC) is one of the abundantly used material in construction industry according to some estimates its usage is only next to water. The primary composition of the Cement Concrete is Ordinary Portland Cement (OPC) and other naturally available raw materials. The production of OPC is environmentally intrusive process because for every ton of cement production equivalent amount of carbon dioxide is released to atmosphere and also about 50% of raw materials procured are deemed not suitable for OPC production (Meyer 2009; Chen et al. 2010; Peng et al. 2013). These lead to various environmental problems such as global warming, leaching in landfills, natural resource exhaustions, excessive mining, etc. This necessitated the adaption of environmentally friendly materials, industrial byproducts, and waste materials, etc., for production of concrete which has same or better properties as compared to CC. Waste materials such as Flyash (FA), Rice-Husk Ash (RHA), sugarcane bagasse ash, silica fume, Ground Granulated Blast furnace Slag (GGBS), etc., have been either used as replacement to cement or as standalone material to produce Geopolymer Concrete (GPC) or alkali-activated slag concretes (Singh et al. 2015; Provis 2014).

The serviceable life of the concrete structure depends on the durability properties of the concrete. Concrete structures exposed to aggressive environments are not serving the intended life as concrete deteriorates faster under such conditions. The hydration products of OPC are factors which influence the durability properties of CC. Geopolymer concrete has good sulfate and acid resistance (Mehta and Siddique 2017; Ban et al. 2017; Wang et al. 2016). The geopolymer concrete incorporated with steel fibers exhibit better flexural strength and tensile strength as compared with GPC without fibers, fiber incorporation also increases the post cracking behavior of concrete increasing the structural integrity of GPC. Most of the GPC are flyash based, the durability studies of GPC with flyash and GGBS have little information in the literature survey, and with this research gap the mechanical and durability properties of the concrete with steel fibers have been investigated.

2 Experimental Procedure

2.1 Materials Used

In this study, geopolymer concrete is prepared by the 50:50 combination of the GGBS and class F flyash for binder. The GGBS was procured from ACC plant and whereas flyash was procured from Raichur thermal power plant. The chemical properties of the binder were determined using X-Ray fluorescence which is presented in Table 27.1. The physical properties such as specific gravity, specific surface area, soundness and loss of ignition are determined according to relevant IS standards are presented in Table 27.2. Manufactured sand (M-Sand) is used for the fine aggregate and 20 mm down angular granite is used for coarse aggregates, both these were procured from locally available sources. The physical properties such as specific gravity, fineness modulus, water absorption, bulk density were determined and are presented in Table 27.3.

Table 27.1 Chemical composition of fly ash and GGBS

Table 27.2 Physical properties of Binder materials

Table 27.3 Physical properties of aggregates

Hooked end steel fibers having aspect ratio of 80 were procured from Chennai was used to prepare Steel fiber-reinforced geopolymer concrete. The impurities present in the steel were tested and are indicated in Table 27.4. The activator used was sodium based which was mixture of 14 M sodium hydroxide and sodium silicate solution. The water glass modulus of the sodium silicate used in the study was about 2.34. The sodium hydroxide solution was prepared from 97% pure NaOH flakes. The ratio of sodium silicate to sodium hydroxide solution was maintained at 2.5.

Table 27.4 Mix proportions of GPC

2.2 Methods

The mix proportion of the geopolymer concrete was done according to Patankar et al. (2015) and the mix proportion considered for the study is indicated in Table 27.5, the mix proportion considered for the study had given excellent compressive strength, flexural and tensile characteristics was considered from previous research (Pulgur et al. 2019). The fresh properties of the concrete were determined using slump test which was done accordance to IS 1199-1959 (1959). Geopolymer concrete specimens were prepared in accordance with IS 516 for compressive strength, flexural strength and split tensile strength. The specimens were cast, covered with plastic sheet and kept in ambient temperature for 24 h and demolded. The specimens were tested for compressive strength on 7 and 28 days according to IS 516-1959, flexural strength in accordance to both IS 516-1959 and split tensile strength on 28 days conforming to IS 516-1959 (1959). The chemical durability properties was conducted in accordance with the Francis et al. (2017), The cube specimens are cured in ambient temperature for 28 days after demolding the initial weight and surface characteristics are noted, then the specimens are immersed in H₂SO₄ and HCl solution whose pH is maintained 1 until the specimens are taken out for testing before which the physical aspects are noted.

Table 27.5 Fresh and mechanical properties of GPC

3 Results and Discussion

3.1 Fresh Concrete Mixes

Fiber reinforced geopolymer concrete was prepared using Flyash and GGBS as the binder materials with steel fiber of weight equal to 2% of binder content. Ability of the flow of concrete and resistance to segregation was measured using slump test. The slump values for different trials are tabulated in Table 27.5.

3.2 Tests on Hardened Concrete Mixes

Compression test. The compression test was carried out using compression testing machine of capacity of 2000 kN as per IS: 516-1959 (Okoye et al. 2017) guidelines. Cubes of dimension 100 × 100 × 100 mm were casted and cured in ambient condition.

The compressive test for the cubes was carried after 7 days and 28 days. The results are tabulated in Table 27.5. From the results presented in Table 27.5, it can be observed that there is 32% increase in the compressive strength from 7 days to 28 days. Presence of the GGBS as the binder material helps in gaining the appreciable compressive strength in first seven days. Addition of GGBS increases the demolding strength of the concrete.

Flexural Strength of Concrete. The flexural strength test was carried out flexural testing machine IS: 516-1959 guidelines. The beams of dimension 100 × 100 × 500 mm were casted and kept in ambient condition. Test was performed after 7 days and 28 days. The results of flexural test are tabulated in Table 27.5. From Table 27.5, it can be observed that

Durability test on Concrete. Durability test was conducted on specimen of 10 cm cubes. The cubes were first air cured for 28 days and were then shifted to the crates containing 1pH solution of HCL and H₂SO₄ (Bakharev 2005; Ganesan et al. 2015). The cubes are placed in the crates for another 28 days. After 56 days loss in density and compressive strength of the concrete blocks were measured and the results are tabulated in Table 27.6. The same procedure was followed after 84 days, i.e., exposure of 56 days. From Table 27.6 it can be observed that there is a decrease in compressive strength of the cube of about 15% when exposed to HCl and 23% when exposed to H₂SO₄. The results of the study are in comparison of the test conducted by Francis et al.

Table 27.6 Variation of density and compressive strength

4 Conclusions

In the current study, the durability effects of SFRGPC exposed to acidic environment are studied experimentally. The following conclusions are drawn:

• The surface of the geopolymer concrete was intact and no loose material was evident as compared CC specimens

• The geopolymer concrete exhibited good resistance when exposed to various acidic environments both in terms of loss in strength and loss in weight

• The loss in weight was only around 2.88% and 3.35% for the GPC specimens exposed to HCl and H₂SO₄ solutions

• The loss in strength was also around 20 and 30% for the GPC specimens exposed to HCl and H₂SO₄ solutions.