Use of laser interferometry for measuring concrete substrate roughness in patch repairs

The overall success and long-term durability of a patch repair is significantly influenced by the bond developed at the interface between the concrete substrate and the repair material. In turn, the bond strength is influenced by the topography (roughness) of the substrate surface after removal of the defective concrete. However, different removal methods of defective concrete produce substrate surfaces with different topographies. Hence, the ability to measure and characterise the topography of substrate surfaces is of great importance for evaluating the effectiveness of different removal methods. In this paper, the effect of two removal methods: electric chipping hammers and Remote Robotic Hydro-erosion (RRH) on the surface roughness is investigated through the use of a prototype non-contact (optical) laser interferometry measuring device. Laboratory results show that the above equipment can be used to characterise substrate roughness and confirm the ability of RRH to create rougher surfaces as opposed to chipping hammers

Bond between microwave cured repair and concrete substrate

The bond strength between a concrete substrate and repair patch is critical to its durability. This paper investigates the effect of microwave curing the freshly applied repair, for 45 min at 132 Watts, on the 28 day bond strength between substrate concrete and different commercial repair materials. The repairs were applied at different ambient temperatures of 20, 10, 2 and −5 °C. Tensile split tests on repaired cube specimens were performed to determine the interfacial bond strength. The ability of microwave curing to prevent the detrimental effects of freezing at early age on the bond and compressive strength of repair patches is investigated. Experimental results show that microwave curing prevents loss of long term (28 day) repair/substrate bond strength of repair materials applied at freezing temperatures (−5 °C), relative to the repairs applied at higher temperatures (2–20 °C), except one lightweight repair formulation. In comparison, the control samples (non-microwave cured) of repairs applied at −5 °C suffered severe loss of bond strength and compressive strength due to early age freezing. In addition, no adverse effects on the bond strength and a small reduction of 6.75% in the 28 day compressive strength are observed in the early age microwave cured repairs applied at ambient temperatures of 2–20 °C. The repair/substrate bond strength is independent of the compressive strength of the repair material at all temperatures of repair application. Microwave curing can accelerate the concrete repair process and facilitate construction activity in cold weather

Pulse velocity assessment of early age creep of concrete

Creep of concrete can have damaging effects by inducing deformations that may contribute or eventually lead to cracks, which influence concrete durability, steel reinforcement exposure to corrosion, and aesthetic damage to architectural buildings. This research investigated the early age creep deformation in concrete samples made with normal, lightweight (Lytag), recycled concrete, and recycled asphalt aggregates using ultrasonic pulse velocity measurements. Creep was achieved by applying a load corresponding to 30% of the strength of concrete to 100 × 250 mm prisms. The compressive load was applied from 24 h after mixing and up to 27 days. The results and analysis of measurements obtained for stress development, specific creep (creep strain per unit stress), and ultrasonic pulse velocity measured up to 27 days after load application are presented. Empirical models that allow the assessment of creep of concrete using ultrasonic pulse velocity measurements are also presented. Early age specific creep is higher for recycled asphalt aggregate than Lytag aggregate and recycled concrete aggregate concretes, which are higher than gravel concrete. Measurements of ultrasonic pulse velocity could be used to determine creep but further work to refine this technique is required

Portland cement, gypsum, and flu ash binder systems characterization for lignocellulosic fiber-cement

The present work aims to obtain an optimal Portland cement, gypsum and fly ash (OPC-G-FA) ternary binder matrix and assess both the addition of paper pulp-by means of mechanical dispersion in aqueous suspension-for cementitious composites reinforcement and the fiber properties over time. To evaluate microfibers preservation from pulp in low-alkaline environments, ternary binder matrices OPC-G-FA are optimized to achieve lower pH values. For that purpose, pH and electrical conductivity over time were analyzed. Only samples with the lowest content in Portland cement (15 20%) offered low alkalinity for short-term. The use of ternary binder systems enhances microfibers conservation compared with control samples (matrices 100% Ordinary Portland Cement) by using FA that, as expected, reduces the presence of Ca(OH)2 in the matrix. Mechanical results prove that obtained matrices yield to a mechanical properties maintenance unlike samples with OPC matrices where toughness is reduced by 95%Financial support for this research project was provided by Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq - Brazil) by means of a grant [351196/2014-5].Mármol De Los Dolores, G.; HOLMER SAVASTANO JUNIOR; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Soriano Martínez, L.; Paya Bernabeu, JJ. (2016). Portland cement, gypsum, and flu ash binder systems characterization for lignocellulosic fiber-cement. Construction and Building Materials. 124:208-218. https://doi.org/10.1016/j.conbuildmat.2016.07.083S20821812

Properties of cement mortar incorporated high volume fraction of GGBFS and CKD from 1 day to 550 days

This study aims to investigate the effect of cement replacement with high volume fraction of ground granulated blast furnace slag (GGBFS) and cement kiln dust (CKD) on mechanical, durability and microstructural properties of cement mortar from 1day to 550 days. Compressive strength and ultrasonic pulse velocity (UPV) were used to evaluate the mortars' performance. Besides, statistical analyses were conducted to predict mortars' mechanical and durability performance as well as investigate the influence of mortars’ properties (mixture and curing time) on their performance. The results indicated that replacing the cement with up to 60% GGBFS and CKD showed a comparable behavior to the cement after 28 days of curing onward. The statistical analysis revealed that the developed models achieved high level of agreement between the predicted and observed results with a coefficient of determination (R2) of more than 0.97. The findings in this study announced on the development of promising binder that can be used in different construction sectors with the benefits of reducing the CO2 emissions