Study of Durability of Concrete with Fly Ash as Fine Aggregate under Alternative Interactions of Freeze‐Thaw and Carbonation

Abstract

To study the durability of concrete with fly ash as fine aggregate subjected to alternative attacks of freeze-thaw and carbonation, the appearance, mass loss, relative dynamic modulus of elasticity, relative compressive strength, and carbonation depth of the concrete are investigated using cyclic tests under single carbonation, single freeze-thaw, and alternation of freeze-thaw and carbonation. In addition, microstructural analysis techniques including scanning electron microscope and X-ray diffraction are adopted to reveal the deterioration mechanism of alternating freeze-thaw and carbonation. Results show that carbonation is beneficial for refining the pore structure and increasing concrete strength in the initial alternative cycle, which delays the damage from freeze-thaw cycles. Damage from freeze-thaw causes crack propagation in concrete, which leads to carbonation intensification. Compared with other test modes, concrete under alternative freeze-thaw and carbonation causes the greatest degree of deterioration during the initial freeze-thaw cycles. The carbonation depth under alternative freeze-thaw and carbonation is positively correlated with the carbonation time and the water-to-cement ratio. However, as the reactant is continuously consumed due to the expansion of crystalline ice and CaCO3, alternative cycles result in the appearance of many more new cracks in the concrete.

Effect of Freeze–Thaw Cycles on Carbonation Behavior of Three Generations of Repeatedly Recycled Aggregate Concrete

“…Similar results have been found in the references of [23,24]. Mao et al [31] reported the durability of recycled fine aggregate concrete under the actions of freeze-thaw and carbonation. The results indicated that crack propagation in concrete caused by the freeze-thaw damage resulted in the carbonation intensification of concrete, while the carbonation refining the pore structure could delay the freeze-thaw damage in the initial cycle.…”

Shrinkage Effects of Using Fly Ash instead of Fine Aggregate in Concrete Mixtures

“…Some studies have indicated that a more viable utilization of fly ash is as a substitute for the fine aggregate in concrete mixtures [4,11]. Contemporary research regarding concrete with fly ash as the fine aggregate (CFA) has focused on the concrete's mechanical properties [12][13][14][15], broadly confirming that the compressive and flexural strengths of CFA are superior to ordinary concrete. Few studies have considered the durability of CFA [15][16][17].…”

“…Contemporary research regarding concrete with fly ash as the fine aggregate (CFA) has focused on the concrete's mechanical properties [12][13][14][15], broadly confirming that the compressive and flexural strengths of CFA are superior to ordinary concrete. Few studies have considered the durability of CFA [15][16][17]. is lack of knowledge regarding CFA durability, and, in particular, its volume stability, limits its practical engineering applications.…”

Effect of Environmental Exposure on the Pore Structure and Transport Properties of Carbon Nanotube-Modified Mortars

“…may result in a significant loss of functionality or excessive and unpredictable maintenance in cementitious materials. For instance, depending on exposure temperature, pore interconnection, and saturation state of the material, the repeated action of freeze-thaw (F-T) cycles may result in the formation of micro-cracks which, in turn, leads to permanent damage [ 1 , 2 , 3 , 4 , 5 ]. Sulfate attack (S-A) is another common type of environmental exposure that causes swelling, fragmentation, and cracking of the cementitious matrix through the reaction of the calcium hydroxide and calcium aluminate hydrate with sulfate ions and the generation of gypsum and ettringite [ 6 , 7 , 8 , 9 ].…”