Cement-based ductile rapid repair material modified with self-emulsifying waterborne epoxy

Experimental study on the properties of a polymer-modified superfine cementitious composite material for waterproofing and plugging

Development of a novel rapid repairing agent for concrete based on GFRP waste powder/GGBS geopolymer mortars

Incompressible debris accumulating in pavement joints or cracks restricts the free expansion of pavement slabs during warm weather and generates excessive compressive stresses along the joint or crack faces. These stresses cause deterioration and spalling of slab corners and edges and accelerate the rate of pavement degradation. Partial depth repair is a preventative maintenance treatment which is commonly used early in the pavement service life to repair spalls and shallow deterioration and restore the intact pavement surface typically before excessive deterioration occurs. The selected repair material must be compatible with the environmental and load conditions. Replacing the deteriorated concrete with a durable material restores the structure integrity, improves the ride quality, and reduces moisture infiltration to subsurface layers of the pavement. The objective of this paper is to evaluate the performance of several rapid setting cementitious concrete repair materials in cold climates and to develop selection criteria for partial depth repair materials. Six repair materials were applied to a test section on a major arterial road in the City of Winnipeg in the summer of 2010. Pre- and post installation detailed condition surveys were conducted at the repair sites and the field evaluation will continue for the next two years. The field performance of the repair materials was evaluated according to: presence of transverse and longitudinal cracks, separation between the material and concrete slab, surface finish of the repair area, and deterioration of the repair material. Laboratory tests were conducted to evaluate the impact of freeze-thaw and wet-dry cycling on the bond strength between repair materials and regular concrete. Concrete cylinders were prepared in the laboratory. The prepared cylinders had a concrete-repair material interface slanted at 30 degrees from the loading axis. The specimens were subjected to freeze-thaw and wet-dry cycling separately. The degradation of the bond strength between repair material and concrete was evaluated from the compressive testing of the bond cylinders at different levels of freeze-thaw and wet-dry conditioning. Results of laboratory and field evaluation will be used to develop performance-based selection criteria for cementitious partial depth repair materials.

Effects of SAE and SBR on properties of rapid hardening repair mortar

One of the key parameters for the performance of concrete repairs is the quality of the interface between the repair material and concrete substrate, which is determined by cement hydration and microstructure development. The moisture exchange between the repair material and concrete substrate plays an important role in the cement hydration and porosity of cementitious repair materials. To better understand the influence of moisture exchange on the hydration of cementitious repair materials, this paper presents a numerical simulation of cement hydration and microstructure development of repair materials, considering moisture exchange. The simulation results reveal that the moisture exchange between the repair material and concrete substrate results in a water content change in two parts. Before the repair material setting, the water absorption of an unsaturated concrete substrate causes a reduction in the w/c ratio in the repair material, decreasing the hydration rate of the repair material. After the repair material setting, the water migrates from the concrete substrate to the repair material to provide additional water to accelerate the hydration of unhydrated cement in the repair material.

Approaches to synthesising rapid geopolymer repair materials made from tannery sludge (TS) and metakaolin (MK) were explored to investigate the treatment and utilisation of TS. The setting time and 1-day compressive strength were taken as indicators for evaluating the performance of the TS/MK geopolymer as a repair material. The effects of the silica/alumina molar ratio (A), sodium oxide/silica molar ratio (B), water/cement (w/c) ratio (C) and TS content (D) were determined, and the durability of the geopolymer was also studied. The optimum formula (A = 2.58, B = 0.33, C = 0.67 and D = 10%) met the requirements for a pavement repair material. The final setting time of the optimum formula was 102 min, the 1-day compressive strength was 21.0 MPa and the chromium leaching concentration was 7.52 mg/l. The geopolymer also exhibited good resistance to high temperatures, acid rain and freeze–thaw processes. A geopolymer repair material that exhibited high early strength and stable performance at later stages was thus synthesised. Microstructure was examined using X-ray diffraction, Fourier transform infrared spectroscopy, mercury intrusion porosimetry and scanning electron microscopy, and it was found that a decrease in geopolymer gelation and increases in the pore size and porosity resulted in a decrease in the properties of the repair material.

Influence of interface and strain hardening cementitious composite (SHCC) properties on the performance of concrete repairs

Evaluation of the bond strength of a novel concrete for rapid patch repair of pavements

Cement hydration and microstructure in concrete repairs with cementitious repair materials

Cracking in concrete repair systems is one of the truly critical phenomena of repair pathology responsible for corrosion, deterioration and failure. The problem of repair cracking has become widespread not only with respect to severe environments which are intensifying restrained volume change stresses but also with respect to repairs in relatively benign environments. Cracking accelerates the penetration of aggressive substances into the concrete and repair material from the exterior environment which in turn aggravates any one or a number of various mechanisms of deterioration. Moisture transport mechanism in the repaired structures is a tool for transferring an outer standard environment into an inner environment, and from one inner environment (existing substrate) into another (repair material). The crack resistance of concrete repair is bearing on three equally important elephants: (1) design details and specifications; (2) repair materials; (3) in-situ workmanship and quality control. This study demonstrates that the properties of cementitious repair materials have to be engineered for dimensional compatibility with existing concrete to improve their resistance to cracking. How good should the cementitious composite material used for repair of existing concrete structures be? How good is good enough. The paper summarized the factors involved and approaches taken when selecting cementitious repair materials. Performance criteria are presented for the selection of dimensionally compatible repair materials and standard material data sheet protocols. The recommended approach can enable material quality improvement, more accurate service life prediction, and satisfactory performance of repaired concrete structures during their intended service life.

Microwave curing of repair patches provides an energy efficient technique for rapid concrete repair. It has serious economic potential due to time and energy saving especially for repairs in cold weather which can cause work stoppages. However, the high temperatures resulting from the combination of microwave exposure and accelerated hydration of cementitious repair materials need to be investigated to prevent potential durability problems in concrete patch repairs. This paper investigates the time and magnitude of the peak hydration temperature during microwave curing (MC) of six cement based concrete repair materials and a CEM II mortar. Repair material specimens were microwave cured to a surface temperature of 40-45 °C while their internal and surface temperatures were monitored. Their internal temperature was further monitored up to 24 hours in order to determine the effect of microwave curing on the heat of hydration. The results show that a short period of early age microwave curing increases the hydration temperature and brings forward the peak heat of hydration time relative to the control specimens which are continuously exposed to ambient conditions (20 °C, 60% RH). The peak heat of hydration of normal density, rapid hardening Portland cement based repair materials with either pfa or polymer addition almost merges with the end of microwave curing period. Similarly, lightweight polymer modified repair materials also develop heat of hydration rapidly which almost merges with the end of microwave curing period. The peak heat of hydration of normal density ordinary Portland cement based repair materials, with and without polymer addition, occurs during the post microwave curing period. The sum of the microwave curing and heat of hydration temperatures can easily exceed the limit of about 70 °C in some materials at very early age, which can cause durability problems.

Calcium sulfoaluminate (CSA) is a comparatively new cementitious material that is mainly established in China where it is produced in a large scale. CSA cement is not covered by European standards. However, it provides different beneficial properties such as rapid hardening and high early strength development. Furthermore, the usage of CSA cement can save energy during production process in comparison to established cementitious materials. Therefore it is also more environmental friendly. Insufficient knowledge of this material behaviour restricts the possibilities and makes further research necessary. The research project applied a laboratory test program to elaborate the characterization of the materials. The obtained knowledge from these tests was then applied to further tests to determine application relevant key properties of CSA based pastes and mortars.The properties of pure CSA cement had been compared with the properties of CSA blends. The additions were PC, HAC, FA and GGBS with quantities of 10, 20 and 30%. The water to cement ratio was varying between 0.4, 0.5 and 0.6. General tests like fineness, XRD and XRF were used to define the present non-standardized material. Investigation of fresh pastes included measurement of setting time and calorimetry. Hardened mortar specimens of different ages were examined for compressive strength. The results showed that CSA itself hardens very rapidly and gives an early strength development. Possible ways of utilization of CSA based mortars and concretes were also emphasized in the paper.

The aim of this research was to study the production of calcium sulfoaluminate (CSA) cement from several industrial waste materials including with marble dust waste, flue gas desulfurization gypsum, ceramics dust waste, and napier grass ash. The chemical composition, microstructure, and phase composition of raw materials were examined using energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), and X-ray diffraction (XRD), respectively. All raw wastes were analyzed using their chemical composition to assign proportion for raw mixture. The raw mixture is calcined at controlled calcination temperatures ranging from 1200 °C to 1300 °C for 30 min. Subsequently, with analysis, their phase composition is calculated by the Rietveld refinement technique. The results suggested that phase composition of clinker calcined at 1250 °C shows the closest composition when compared to target phases, and was selected to prepare CSA cement. The FTIR analysis was performed to study the hydration processes of CSA cement. The Ordinary Portland cement (OPC) based with adding CSA cement between 20 wt.% and 40 wt.% were investigated for the effect of CSA cement fraction on water requirement, setting times and compressive strength. The results showed that rapid setting and high early strength can be achieved by the addition of 20–40 wt.% CSA cement to OPC.

The slant shear test highlighted by British Standard 6319 No. 4 was used to evaluate the bond strength between selected repair materials and parent concrete. Seven resinous and six cementitious repair materials were used to repair fractured specimens. Repaired test specimens were aged by subjecting them to heat-cool cycles that simulated repeated extreme summer day in the southern part of the United States (e.g., Mississippi). The results of thermal cycling showed a strong correlation between the difference in the coefficient of thermal expansions, as well as the difference in elastic moduli, between repair materials and concrete, and the reduction in bond strength. Although resinous materials possessed a higher bond strength to concrete, they showed higher reduction of bond strength than cementitious materials.

Addressing the current lining cracking problem in coastal tunnels, this paper independently introduces a novel type of repair material for tunnel lining cracks—the composite repair material consisting of waterborne epoxy resin and ultrafine cement (referred to as EC composite repair material). Through indoor testing, we have analyzed the change rule of the mass change rate, compressive strength, flexural strength, and chloride ion concentration of the repair material samples in erosive environments, with the dosage of each component in the EC composite repair material being varied. We have also investigated the working performance, mechanical properties, and microstructure of the repair material. The results of this study show that when the proportion of each component of ultrafine cement, waterborne epoxy resin, waterborne epoxy curing agent, waterborne polyurethane, defoamer, and water is 100:50:50:2.5:0.5:30, the performance of the EC composite repair material in a chloride ion-rich environment is optimal in all aspects. When the mixing ratio of each component of the EC composite repair material is as stated above, the repair material exhibits the best performance in a chloride ion erosion environment. With this ratio of components in the EC composite repair material, the fluidity, setting time, compressive strength, flexural strength, and bond strength of the repair material in a chloride ion erosion environment can meet the requirements of relevant specifications, and it is highly effective in repairing tunnel lining cracks. The polymeric film formed by the reaction between the waterborne epoxy resin emulsion and the curing agent fills the pores between the hydration products, resulting in a densely packed internal structure of EC composite repair material with enhanced erosion resistance, making it very suitable for repairing cracks in tunnel linings in erosive environments.