Improving Freeze–Thaw Resistance of Concrete Road Infrastructure by Means of Superabsorbent Polymers

Bart Craeye, Geert Cockaerts, Patricia Kara De Maeijer
2018 Infrastructures  
The scope of the paper is to report an investigation on durability of infrastructure concrete for roads and bridges by creating a size and shape-designed pore systems in concrete in order to improve it, especially in terms of freeze-thaw resistance. By means of this experimental laboratory study, an alternative for usage of air entrainment agents (AEA) in concrete infrastructures was found in the way of using superabsorbent polymer materials (SAPs). The effect of the addition of SAPs of
more » ... t amounts and different types into fresh concrete mix was investigated, including: compressive strength tests, weight loss measurements, visual and microscopic inspections and scanning electron microscopy (SEM) analysis. The detrimental strength reduction effect was not observed. The freeze-thaw procedure was varied, using different types of de-icing salts and heating/cooling regimes. It can be concluded that an improvement of the freeze-thaw resistance of concrete infrastructure depends on the particle size and optimal amount of SAPs added into concrete mix. The addition of 0.26 wt % of dry SAPs into the fresh concrete reference mix led to the significant decrease of scaling up to 43% after 28 freeze-thaw cycles. Both dosage and particle size of the SAPs had a significant impact on the obtained results and the freeze-thaw resistance in this experimental laboratory study. In this code, the concrete composition restrictions are listed (water-to-cement ratio, choice of cement type and amount, minimal compressive strength, water absorption ratio and scaling/exfoliation), in order to come to a durable concrete application. In practice [3], a lot of damage of the Belgian concrete roads is visible. According to Jones et al. [2] freeze-thawing is the second main deterioration process affecting the concrete's durability, besides steel corrosion in reinforced concrete elements. The main factors contributing to concrete failure are the impact of the environment, poor concrete quality, and insufficient handling and curing of the freshly cast concrete. During harsh Belgian winters under condition of negative temperatures, cycles of freezing and thawing, and in combination with the use of de-icing salts, concrete infrastructure (roads and bridges) suffers from scaling, which increases the roughness of the surface with following decrease of the thickness of the concrete pavement and internal mechanical degradation due to freeze-thaw attack [6] . This exfoliation of the outer concrete layers results in a reduction of durability, comfort and safety of its practical application [6] . Dooms et al. [3] also mentioned that in the case where supplementary cementitious materials (SCMs) such as blast furnace slags and fly ashes are used, the effect of the curing duration and handling is of major importance in order to come to a durable and frost resistant concrete. In cases where de-icing salts are used, the impact of the freeze-thaw effect is worsened, mainly due to the scaling effect (chlorides lower the freezing point and the temperature gradient due to the de-icing effects leading to exfoliation of the outer concrete layer) and the osmotic pressure (due to salt concentration gradient). In order to overcome internal mechanical degradation, concrete has to contain small cavities/pores in the concrete matrix which form a connecting network of pressure vessels. This network of pores can react to increasing pressure of the freezing water reducing the tension pressure in the upper and inner concrete layers. In SB250 [5], the standard measure to overcome frost damage (with or without the use of de-icing salts), is the use of air entrainment agents (AEA) for a durable concrete. It is well known that inducing additional air into a concrete matrix leads to reduction of the tensile and compressive strength of the material (one percent induced air leads to a roughly five percent strength reduction) [7] . In Belgium, in the case of traditional concrete, air entrainment agents (AEA) are added into concrete mix in order to increase resistance against freeze-thaw actions. In the case of heavy load bearing structures, addition of AEA into concrete mix is not desirable since it gives significant strength losses [7] . An improvement in degradation resistance of concrete pavements can be obtained by modifying the composition of the considered pavement or its components. The use of fibers and/or polymer modified binders in asphalt has proven to be very efficient for concrete layers [8] . A study conducted by [9] mentioned the improvement of frost scaling resistance by replacing Ordinary Portland Cement (OPC) of the reference concrete mix with fly ash (FA) and/or silica fume (SF) (up to 15% by weight of cement). However, it was noted that scaling values of the FA specimens without SF were less than control specimens' scaling, but they did not satisfy the capillary suction, se-icing agent and freeze-thaw-test (CDF) criterion. The obtained ternary concrete mix with 15% OPC replacement with 10% of fly ash and 5% of silica fume showed a significant reduction up to 50% of the scaling. This was also confirmed by Dooms et al. [3] evaluating the scaling of concrete (W/C-ratio of 0.45, 340 kg of added cement) with various cement types. In the case where sufficient curing (56 days under water) of the specimens was applied, specimens containing blast furnace slag clearly performed better compared to the ones containing OPC. The difference between specimens that were cured in open air (relative humidity of 60%) was much smaller. In practice [3], concrete infrastructure elements using blast furnace slag cements or other supplementary cementitious materials suffer severely from freeze-thaw actions, especially in cases where the curing time was insufficient. As an alternative solution for the improvement of scaling resistance, the use of superabsorbent polymer materials (SAPs) can be recommended. SAPs are cross-linked hydrogel networks consisting of water-soluble polymers which generally are composed of ionic monomers and need a low cross-linking density in order to create a large fluid uptake capacity. SAPs can take up and hold aqueous solutions up to several hundred times their own weight while retaining it even under pressure [10] . As the SAPs will release their water during hardening, they will leave behind air-filled pores. During freeze-thaw
doi:10.3390/infrastructures3010004 fatcat:w5nykaobw5gxbnvywcgqgluaiq