Evaluation of Polymer Modified Mortar and Bonding Agent for Structural Repair

Polymer modified mortar is found to be suitable for structural repair and strengthening of damage structural elements. Conventional mortar is not preferred in repair of concrete since it has inferior mechanical property and durability performance. Polymer based mortar is an alternative to conventional mortar with enhanced mechanical properties. However, there are limited specifications and guidelines available for specifying PMM mixes for structural repair work. The research work aims to evaluate the mechanical performance of polymer based mortar with varying concentration of styrene butadiene rubber latex at laboratory scale. Another aspect in repair of corrosion damage structures is the bond between the substrate concrete and repair mortar. In order to study the effectiveness of bonding agents, the performance evaluation of bonding agents has been evaluated using slant shear test and pull-off test as per ASTM C 882 and EN 1542 respectively. Findings of study indicates that at 8-10 percent concentration of dry polymer solid by cement mass in polymer based mortar is the optimum dosage. Styrene-butadiene rubber based polymer mortar showed improvement in flow in comparison to normal mortar however, mixes with crushed sand shows decrease in flow which is due to presence of more fines. Slant shear and pull-off test method shows epoxy bonding agent give better bond strength as compared to SBR latex.

On the Calibration of a Numerical Model for Concrete-to-Concrete Interface

The study was devoted to the numerical modelling of concrete-to-concrete interfaces. Such an interface can be found in many modern composite structures, so proper characterisation of its behaviour is of great importance. A strategy for calibration of a model based on cohesive finite elements and the elastic-damage traction–separation constitutive law available by default in the Abaqus code was proposed. Moreover, the default interface material model was enhanced with the user-field-variables subroutine to include a real strength envelope for such interfaces. Afterwards, the modelling approach was validated with numerical simulation of the most popular tests for determining the strength characteristics of concrete-to-concrete interfaces: three-point bending beam with a notch, splitting bi-material cubic specimens, and slant-shear tests. The results of own pilot studies were used as well as those reported by other researchers. The performed simulations proved the accuracy of the proposed modelling strategy (the mean ratio of ultimate forces obtained with numerical models and from experiments was equal to 1.01). Furthermore, the presented examples allowed us to better understand the basic test methods for concrete interfaces and the observed mechanisms of failure during them.

Bond Strength Analysis of Repaired Concrete based on Polymerization of Glycoluril Formaldehyde

Repairing old concrete include the correct choice of material and methodology adopted which may not affect the quality providing monolithic condition for old and new concrete. This study investigates two different parameters such as the impact as well as the optimum usage of new polymer glycoluril-formaldehyde as bonding material. Second one is about to understand the surface preparation for increased bonding strength at the interfacial area of old and new concrete. Five different types of surface textures are used to estimate the bond strength such as plane, lined, waved, grid and chipped. Glycoluril aids as a bonding material in both old and new concrete, and it is introduced at 0%, 1%, 2%, 3%, and 4% into the cement mixture. When the surface preparation creates a rough surface, it helps in repairing the concrete with the help of polymerization of glycoluril formaldehyde which promotes the enhancement of bond strength and slant shear. The bond strength of the specimens was measured by slant shear method in compression as well as tension for a period of 1, 2 and 4 weeks of new concrete. The results indicated that the highest bond strength was achieved in 3 percentage addition of glycoluril and grid patten substrate preparation.

Prediction of the Interface Shear Strength between Ultra-High-Performance Concrete and Normal Concrete Using Artificial Neural Networks

The bond strength between ultra-high-performance concrete (UHPC) and normal-strength concrete (NC) plays an important role in governing the composite specimens’ overall behaviors. Unfortunately, there are still no widely accepted formulas targeting UHPC–NC interfacial strength, either in their specifications or in research papers. To this end, this study constructs an experimental database, consisting of 563 and 338 specimens for splitting and slant shear tests, respectively. Moreover, an additional 35 specimens for “improved” slant shear tests were performed, which could circumvent concrete crushing and trigger interfacial debonding. Additionally, for the first time in our tests, the effect of casting sequence on UHPC–NC bond strength was identified. Based on the database, an artificial neural network (ANN) model is proposed with the following inputs: namely, the normal stress perpendicular to the interface, the interface roughness, and the compressive strengths of the UHPC and NC materials. Based on the ANN analyses, the explicit expression of UHPC–NC bond strength is proposed, which significantly lowers the prediction error. To be fully compatible with the specifications, the conventional shear-friction formula is modified. By splitting the total force into adhesion and friction forces, the modified formula additionally takes the casting sequence into account. Although sacrificing accuracy to some extent compared to the ANN model, the modified formula relies on a solid physical basis and its accuracy is enhanced significantly compared to the existing formulas in specifications or research papers.

Interfacial Bond Properties between Normal Strength Concrete and Epoxy Resin Concrete

It is necessary to pay attention to the bonding strength of the interface between precast normal strength concrete (NSC) and cast-in-place epoxy resin concrete (EMR) when using EMR as a repair or filling material or an overlay in bridges’ rehabilitation. However, the performances of epoxy concrete are different due to differential mix ratios; thus, the bonding properties between various epoxy resin concrete and cement concrete are not completely the same. This article investigated the interfacial bond properties between NSC and ERC by direct tensile, push-out, and slant shear test with specimens of special size and structure and observed the interfacial bond strength and corresponding failure modes. The minimum bond strength under direct tension was 0.72 MPa, while the minimum bond strength was 1.71 MPa and 3.19 MPa for the push-out test and slant shear test, respectively. Results indicated that the slant shear test specimens with an inclination angle of 45° are not suitable for the slant shear test due to higher compressive stress. Furthermore, the cohesion and friction coefficient of interface bond strength were calculated inversely in accordance with the results obtained from the corresponding direct tensile and slant shear tests. The minimum cohesion value was 1.71 MPa, and the minimum friction coefficient value was 0.46.

Evaluating the bond strength of repair materials under harsh environmental loading

When considering aging infrastructure, repair paths are often taken as a cheaper solution to extend the life the structure. Repair materials are selected for their sustained capacity to withstand the load. This study evaluated the durability of repair materials, based on the principles of engineered cementitious composites against traditional concrete mixes. The durability of the repair materials was evaluated through a comprehensive testing regime which evaluated the performance of the materials in isolation as well as in combination with a prescribed substrate. While the SCM based repair mixes withstood durability tests comparability and did outperform the reference concrete, the improvement wasn’t significant enough to justify the costs associated. The slant shear method may not be the optimal way to measure bond strength as a valid result is greatly dependent on the ratio of bond to compressive strength for the mix in question. Additional testing is recommended.

Evaluating the bond strength of repair materials under harsh environmental loading

When considering aging infrastructure, repair paths are often taken as a cheaper solution to extend the life the structure. Repair materials are selected for their sustained capacity to withstand the load. This study evaluated the durability of repair materials, based on the principles of engineered cementitious composites against traditional concrete mixes. The durability of the repair materials was evaluated through a comprehensive testing regime which evaluated the performance of the materials in isolation as well as in combination with a prescribed substrate. While the SCM based repair mixes withstood durability tests comparability and did outperform the reference concrete, the improvement wasn’t significant enough to justify the costs associated. The slant shear method may not be the optimal way to measure bond strength as a valid result is greatly dependent on the ratio of bond to compressive strength for the mix in question. Additional testing is recommended.

Bond Strength and Flexural Capacity of Normal Concrete Beams Strengthened with No-Slump High-Strength, High-Ductility Concrete

This study investigates the flexural behavior of normal-strength concrete (NSC) beams that were strengthened with no-slump, high-strength, high-ductility concrete (NSHSDC). A set of slant shear tests was performed to investigate the initial performance of the NSC substrate strengthened with NSHSDC. Slant shear tests considered two types of roughness of interface and five angles of the interface between NSC and NSHSDC. The test results showed that except for specimens with a 75° interface angle, the specimens with high roughness were conformed to the properties (14–21 MPa for 28 days) of the ACI Committee 546 recommendation. For flexural strength tests, NSC beams strengthened with an NSHSDC jacket on the top and bottom sides, three sides, and four sides resulted in strength increments of about 8%, 29%, and 40%, respectively, compared to the beams without NSHSDC jacket. Therefore, the use of NSHSDC is an effective method to improve the performance of NSC beams and is recommended for strengthening reinforced concrete members.