Effects of Erosion Form and Admixture on Cement Mortar Performances Exposed to Sulfate Environment

Abstract

The effects of the admixtures, erosion age, concentration of sulfate solution, and erosion form of sulfate attack on the mechanical properties of mortar were investigated. Simultaneously, the microstructure, pore characteristics, kinds and morphologies of erosion products of mortar before and after sulfate attacks were performed by Mercury Intrusion Porosimetry (MIP), Environment Scanning Electronic Microscope and Energy Dispersive Spectrometer (ESEM-EDS). In addition, the crystal form and morphology characteristics of crystallization on mortar surfaces attacked by partial immersion form were studied. The results showed that the compressive and flexural strengths of mortar attacked by sulfate for four months decreased with the increase of the replacement of cement with fly ash, and the corresponding strength of mortar containing slag first increased and then decreased. The admixtures can improve the microstructure and mechanical properties of mortar within the replacement ratio of 10%. Although the change laws of the mortar specimens containing different admixtures were similar, the mortar containing slag had an excellent sulfate resistance under the same condition. Compared with the complete immersion form, the strength variation of the mortar containing fly ash attacked by semi-immersion form was less. The porosity and average pore diameter of mortar attacked by sulfate for four months increased, and the percentage of micropore with the pore diameter less than 200 nm increased. Plenty of rod-like and plate-like erosion products were generated in mortar attacked by a sulfate solution with a high concentration. A larger number of fibrous and flocculent crystallization covered the mortar’s surface containing fly ash, but it was a granular and dense crystallization formed on the mortar’s surface containing slag. Much dendritic erosion product was generated in the mortar attacked by semi-immersion form, and ESEM-EDS analysis revealed that it may be scawtite, spurrite, and residue of the decomposed calcium silicate hydrate (CSH) in the inner mortar; however, the crystallization sodium sulfate was crystallized on mortar surface.

Variation of Critical Water Pressure for Hydraulic Fracturing in Cement Mortar under Sulfate Attack

“…where E c is the elastic modulus of the cement mortar matrix. When the porosity n = 0, the circumferential average strain ε c within the cement mortar matrix can be expressed by Equation (10).…”

“…The long-serving environment of hydraulic structures is very complex, it often has chloride ions, sulfate ions, and sodium ions, hydrogen ions and so on. Sulfate ion as a common corrosive ion, which can result in undermining the structural integrity and shortening service life of hydraulic structures [8][9][10]. When the sulfate ions penetrate into cement mortar and react with the hydration products to produce expansive products.…”

Crystallization Cycles in Masonry Walls: Experimental Technique to Develop Accelerated Aging on a Real Scale

“…In pursuit of this, an accelerated aging technique based on sodium sulfate crystallization cycles is employed (Cultrone and Pardo, 2008;Rivas Brea et al, 2008); where utilizes the efflorescence capacity of sodium sulfate, which crystallizes within the porous network of the materials and induces significant degradation. This test involves cyclic saturation of material samples in a sodium sulfate solution, followed by drying in an oven and standing at room temperature to record data (Liu et al, 2020;Morales Tassinari et al, 2020). This crystallization simulates accelerated wear due to moisture and facilitates the evaluation of corrective systems (Speri et al, 2017).…”

An Experimental Study on Mechanical Properties for the Static and Dynamic Compression of Concrete Eroded by Sulfate Solution

“…Sulfate erosion usually occurs in the form of swelling and cracks in concrete [10], when after cracking, carry sulfate solution easier penetration into concrete internal pore [11], sulfate erosion in strength and durability of the concrete after key performance are affected. Under these conditions, sulfate erosion can compromise some mechanical properties of concrete [12,13]. Therefore, for related construction works and marine engineering, the durability of the overall structure will be reduced by sulfate erosion of concrete, resulting in the weakening of concrete and endangering life and property.…”