Water and sewer water pipes are usually exposed to highly aggressive media attacks. Therefore, there is an increasing need for new construction materials distinguished by high durability under aggressive media attacks rather than ordinary Portland cement. The most common disadvantages of ordinary Portland cement are environmental pollution from gas emission during the cement industry, deterioration under aggressive media attacks, and high cost. Geopolymer binder can be used in waste-water and water pipes more than phase like in concrete as a construction material or in mortar as a rehabilitation material in waste-water and water pipes [1, 2]. Geopolymers, classified as inorganic aluminosilicate polymers, are characterized by their high performance and low unit volume weight. Geopolymer composites have recently found wide use in many applications of constructions in addition to in repairing and strengthening buildings because of their high strength, environmental friendliness, and significant cost advantages [3,4,5].
RC pipes are widely used in infrastructure as they are characterized by their reliable long-term performance. The pipe may contain up to three welded reinforcement cages so as to withstand anticipated loads. The amount of welded reinforcement cages depends on multiple parameters (e.g., pipe diameter, pipe wall thickness, required strength, etc.) [6]. Using double spiral stirrups in the concrete of drainage pipes provides uniform constraint function and upgrades the resistance to deformation ability of drainage pipe [7]. During the loading process, pipes develop vertical and horizontal cracks on interior surfaces (crown and invert) and mid-height on exterior surfaces (spring lines), respectively. The locations of the crown, invert, and spring lines are shown in Fig. 1. To improve the service life of pipes in an aggressive sewer environment and limit their maintenance requirements, the cover thickness of pipes must be increased. So, using one layer of steel reinforcement in pipe design is better than using two layers to provide more concrete cover for the reinforcing steel [8].
The mechanism of corrosion of reinforcing steel in concrete is defined as an electrochemical process. The surface of the corroding steelworks is a composite of the anode and the cathode electrically connected through a body of steel itself. The factors which affect the corrosion of steel in concrete structures are aggregate size and its grading, the thickness of concrete cover over reinforcing steel, impurities in mixing and curing water, contaminants in aggregate, chloride ions that reach the rebar level either through the concrete ingredients or from the external environment, carbonation and entry of acidic gaseous pollutants to rebar, temperature and relative humidity, cement composition, presenting of oxygen, and moisture at the rebar level [9, 10]. Several studies focused on the corrosion process by accelerated corrosion setup in different RC element applications [11,12,13,14,15,16,17]. The effect of a bond impairment is more effective than the decrease in the cross-sectional area of bars on the loss of tension force capacity [13]. During the pull-out test on corroded bars, an increase in the load-carrying capacity of slabs with a small amount of corrosion was recorded. A steady loading carrying capacity at 1% diameter loss was recorded, and then a decrease in loading carrying capacity at 2% diameter loss started.
The production of geopolymer concrete is by reacting an alkaline liquid with a source material rich in silica and alumina such as slag, fly ash, red mud, and silica fume. Geopolymer binder is used in many phases as an example; paste, mortar, and concrete in many investigations [18,19,20,21,22]. The most crucial feature of geopolymer concrete as new material is its high resistance to aggressive media attacks. Geopolymer mortar was used as a spray which forms a crystalline structural solution for increased resistance to acids and surface durability. It is characterized by fast curing, which allows the pipe to be rehabilitated quickly. In addition to fast curing, it is characterized by environmental effects resistance such as heat and cold [18]. By applying splitting, shear, significant cracking, and conical type failure tests on geopolymer mortar specimens, the geopolymer mortar specimens can be classified as brittle material [19]. Comparing geopolymer concrete to ordinary cement concrete in the case of precast units, geopolymer concrete is more environmentally friendly and economical than ordinary cement concrete [20].
Furthermore, geopolymer concrete has better workability than ordinary cement concrete of the same grade [21]. The amount of water and binder required in geopolymer concrete is less than regular cement concrete of the same grade workability level and the same compressive strength at 28 days [21]. After exposure to sulfate attack such as magnesium sulfate, the P.H. value of the solution, which contain geopolymer specimens, increase slightly during the first 14 days and after that has not changed [22,23,24,25].
The objective of the present research is to conduct an experimental study to investigate the different mixes of geopolymer mortar and concrete to achieve the optimum concrete mix for pipes. The effect of aggressive media (magnesium sulfate and chloride) and accelerated corrosion periods on the corrosion rate and infrared analysis (FTIR) of RC pipes were studied. This research sheds light on replacement OPC binder by geopolymer binder in different cases such as mortar and concrete. The comparison between the compressive strength of geopolymer and OPC mortar and concrete was recorded. The corrosion behavior of the reinforcing steel embedded in pipes is evaluated by using the Voltalab test. The microstructure of concrete was observed by scanning infrared analysis (FTIR). The paper also introduces the experimental program details containing the preparation of samples, casting of concrete, and curing technique. The details of the accelerated corrosion setup technique are presented; then, the results obtained from the performed experimental program are presented and discussed. The novelty of this research is that it shed light on the advantage of using geopolymer mixes in RC pipes, such as high strength performance, corrosion resistance, low cost, and environment-friendliness compared with OPC mix in RC pipes. Many researchers have also investigated the behavior of geopolymer material in an aggressive environment. However, it is infrequent to present the effect of geopolymer mixes in RC pipes after a long time of exposure to an aggressive environment by applying accelerated corrosion set up for three months on pipes. In addition, this study includes more than one aspect, such as geopolymer, engineering, chemistry, and material science.