Surface Treatments for Concrete Under Physical Salt Attack

Physical salt attack (PSA) is a key deterioration mechanism for concrete structures in contact with salt-rich media. Yet, procedures and techniques for protecting and repairing concrete affected by PSA are not adequately addressed in the technical literature. Therefore, in this study, three surface coatings of concrete were tested to determine their ability to withstand conditions stimulating to PSA. The treatments were selected to achieve either a single function such as acting as a membrane layer or hydrophobic agent, or combined pore blocking and water repelling functions. Coatings were applied on a concrete mixture typically used for residential foundations in Canada. Mass change was used as a measure to quantify the damage, in addition to microscopy and mineralogical analyses to elucidate the damage mechanisms. The results showed that the damage in deteriorating specimens was due to a combination of physical and chemical sulfate attacks. Also, epoxy and ethyl silicate were effective at protecting concrete from sodium sulfate damage while silane was not

MAT-704: RESISTANCE OF CONCRETE INCORPORATING PORTLAND LIMESTONE CEMENT TO SULFURIC ACID

Concrete has long been the most popular choice for constructing key infrastructural elements such as sewer pipes, water treatment facilities, industrial floors and foundations. However, many field cases from all around the world have shown that concrete elements in these environments are severely damaged due to biogenic and/or chemical sulfuric acid attack. Since high alkalinity is required for the stability of the cementitious matrix, concrete is highly prone to acid attacks, which decalcify and disintegrate the hydrated cement paste to various levels based on exposure conditions and type of concrete. Numerous studies have been conducted to enhance the durability of concrete and understand the influence of key mixture design parameters on its resistance to sulfuric acid attack. Yet, there is dearth of information on the behaviour of a new type of cement in North America, which contains a high level (5 to15%) of interground limestone powder (portland limestone cement: PLC), under acidic attack. Hence, the aim of this study is to investigate the effect PLC with or without supplementary cementitious materials (SCMs) on the durability of concrete exposed to acidic attack. The study comprised 13 weeks (90 days) immersion of test specimens in 5% sulfuric acid solutions with pH in the range of 0.1 to 2.5. Physical and microstructural results reveal that PLC may improve the resistance of concrete to sulfuric acid attack, whereas the SCMs had a mixed effect on the results

Post-Cracking Behavior of Cementitious Composite Incorporating Nano-Silica and Basalt Fiber Pellets

Recently, fiber reinforced polymers (FRPs) have been increasingly used to reinforce concrete structures in harsh environments, due to their non-corrodible nature. Developing a nonferrous reinforcement system (corrosion-free system) for concrete using FRP bars along with discrete fibers is a promising option for exposed concrete structures in cold regions or marine environments. Incorporating highly efficient non-metallic fibers into any cementitious composite is capable of reducing bleeding, controlling shrinkage cracking, and improving toughness and impact resistance. Therefore, in this study, a new type of basalt fiber pellets with high tensile strength was investigated. This paper reports on the flexural performance of the basalt fiber-reinforced cementitious composite (BFRCC) compared to steel fiber-reinforced cementitious composite (SFRCC). The cementitious composite incorporated general use cement, slag and nano-silica. The key mechanical property determined was the post-cracking behavior in terms of residual strength, and toughness. Standard prisms (100 × 100 × 350 mm) were cast using basalt fiber pellets and steel fibers with three different dosages and tested after 28 days following the general guidelines of ASTM C1609 (Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete). Analysis of results showed a high level of effectiveness of the basalt fibers to enhance the post-cracking behavior of specimens, as they behaved comparably or superiorly (first cracking, load-deflection relationship, and toughness) to counterpart specimens comprising steel fibers

MAT-705: IMPROVING THE EFFICIENCY OF ZINC SACRIFICIAL ANODES IN REPAIRED CONCRETE

Zinc sacrificial anodes are considered an effective and economical method to prevent the electrochemical corrosion of steel bars by providing cathodic current to bars, which can provide corrosion protection at low galvanic current densities in the range of 0.2 to 2 mA/m2. Sacrificial anodes are commonly used in RC structures particularly in bridge decks to mitigate a critical phenomenon that occurs in the original concrete beside the repaired patches, which is known as the ‘halo effect’. One of the key factors affecting the efficacy of zinc anodes is the resistivity of concrete or cementitious repair material in which these anodes are embedded. There is a general notion that the higher the electrical resistivity of concrete or repair material, the less likely that zinc anodes produce the target galvanic current for optimum protection of steel bars. However, no systematic data are available on the maximum allowable electrical resistivity of repair materials/concretes beyond which zinc anodes cannot properly function to prevent corrosion. The specific objective of this study is to explore the effect of concrete resistivity on the efficiency of zinc anodes at mitigating patch accelerated corrosion (halo effect). Concrete slabs were cast to simulate the patch repair technique in the field, and the main parameter in this research was changing the resistivity of the repair section in the slabs (5,000, 15,000, and 25,000 Ω-cm). Analysis of results shows a high level of effectiveness of the anode to prevent corrosion up to 20 weeks under a wetting-drying exposure

Properties of Fiber-Reinforced Mortars Incorporating Nano-Silica

Repair and rehabilitation of deteriorating concrete elements are of significant concern in many infrastructural facilities and remain a challenging task. Concerted research efforts are needed to develop repair materials that are sustainable, durable, and cost-effective. Research data show that fiber-reinforced mortars/concretes have superior performance in terms of volume stability and toughness. In addition, it has been recently reported that nano-silica particles can generally improve the mechanical and durability properties of cement-based systems. Thus, there has been a growing interest in the use of nano-modified fiber-reinforced cementitious composites/mortars (NFRM) in repair and rehabilitation applications of concrete structures. The current study investigates various mechanical and durability properties of nano-modified mortar containing different types of fibers (steel, basalt, and hybrid (basalt and polypropylene)), in terms of compressive and flexural strengths, toughness, drying shrinkage, penetrability, and resistance to salt-frost scaling. The results highlight the overall effectiveness of the NFRM owing to the synergistic effects of nano-silica and fibers

Properties of concrete incorporating nano-silica

This study investigated the effect of colloidal nano-silica on concrete incorporating single (ordinary cement) and binary (ordinary cement + Class F fly ash) binders. In addition to the mechanical properties, the experimental program included tests for adiabatic temperature, rapid chloride ion permeability, mercury intrusion porosimetry, thermogravimetry and backscattered scanning electron microscopy in order to link macro- and micro-scale trends. Significant improvement was observed in mixtures incorporating nano-silica in terms of reactivity, strength development, refinement of pore structure and densification of interfacial transition zone. This improvement can be mainly attributed to the large surface area of nano-silica particles, which has pozzolanic and filler effects on the cementitious matrix. Micro-structural and thermal analyses indicated that the contribution of pozzolanic and filler effects to the pore structure refinement depended on the dosage of nano-silica

Utilization of Novel Basalt Fiber Pellets from Micro- to Macro-Scale, and from Basic to Applied Fields: A Review on Recent Contributions

Fiber-reinforced cementitious composites (FRCC) are one of the leading engineering materials in the 21st century, as they offer proficiency in enhancing strength, ductility, and durability in structural engineering applications. Because the recently developed basalt fiber pellets (BFP) offer combined strands of fibers encased in a polymer matrix, they are being prevalently studied to explore new possibilities when used in brittle materials such as mortar and concrete. Hence, this paper synthesizes the intensive research efforts and contributions to this novel class of fibers conducted by the authors. Specifically, it reviews the fresh, mechanical, and durability properties of FRCC incorporating single BFP or hybrid with polyvinyl alcohol fibers and modified with slag/fly ash and nano-materials and its suitability for different field applications. In addition, the nano- and meso-scale modeling of such matrices are described. BFP significantly contributes to improving post-cracking flexural behavior by toughening the cementitious matrix and minimizing strength losses when exposed to harsh environments. All results show promising progress in the development of high-performance FRCC comprising BFP, with potential success for structural and pavement applications