Concrete Strengthening by Introducing Polymer-Based Additives into the Cement Matrix—A Mini Review

The modern types of concrete are a mixture of aggregates, cement, water and optional additives and admixtures. In particular, polymer additives seem to be a promising type of component that can significantly change concrete and mortar properties. Currently, the most popular polymer additives include superplasticizers, latexes and redispersible powders. Moreover, in order to improve the properties of concrete-based composite admixtures, which enhance the resistance to cracking, polymer fibres and recycled polymers have been researched. All the types of polymeric materials mentioned above are broadly used in the construction industry. This work summarizes the current knowledge on the different types of popular polymeric additives. Moreover, it describes the correlation between the chemical structure of additives and the macro-behaviour of the obtained concrete.

Experimental and Analytical Studies on Strengthened Axially Loaded RC Columns

The strengthening and retrofitting of concrete structures are becoming an essential part of the building and its structures. When the building comes of age, there is a need to increase the structural members' strength, life, and resistivity against unfavorable environmental conditions. In the current scenario, ferrocement composites are used for structural strengthening and rehabilitation. Therefore, an experimental investigation is needed to evaluate the effectiveness of the strengthening on the square and circular reinforced concrete columns by ferrocement and micro concrete materials. The experimental results showed that the ferrocement and micro concrete techniques enhanced the stress-strain behavior and displacement limit of the square and circular RC column. The strengthening circular RC column by micro concrete gives a better performance in stress-strain behavior and displacement limit. In addition, the ferrocement and micro concrete strengthening technique is a promising and economical alternative compared to the other strengthening techniques. Also, test results were compared with ACI and CNR–DT representative load-carrying models to verify each model's reliability and accuracy. Furthermore, the TOPSIS method was adopted to find out the best solution for square and circular columns, and cost analysis was carried out. HIGHLIGHTS RC columns were strengthened using ferro cement and micro concrete RC Columns under compressive concentric load were tested Micro concrete strengthening controls deflection and enhances the load capacity of columns The analytical approach of TOPSIS was used to find the best solution GRAPHICAL ABSTRACT

Study on the compensating calcium ion method for existing concrete based on crystal infiltration waterproof materials

The quality of the the existing concrete surface in its repairing and strengthening is the key factor affecting the together working performance. The effective method to solve this problem is to use permeable crystal waterproof material to strengthen the existing concrete surface. In view of the existing old concrete which lacks free Ca2+ in the interior, the method of compensating calcium ion strengthening is proposed based on the action mechanism of permeable crystalline waterproof material. On the basis of DPS, calcium ion compensating agent Ca (OH)2, Na2SiO3 (sodium silicate) and Na2CO3 (potassium carbonate) solutes are added to prepare composite reinforcement solution for impregnation strengthening of concrete. Scanning electron microscopy (SEM) was used to observe the microstructure of the concrete before and after strengthening. It showed that after the entry of silicate ions, C-S-H colloid was formed by reaction with Ca (OH)2, and C-S-H gel blocked some pores, which made the inner microstructure more compact. The results of compressive strength before and after concrete strengthening show that the strengthening effect of calcium ion compensation method for low-strength concrete is better than that of permeable crystallization material strengthening method. The strength of C5 and C15 grade concrete is increased by 36.1% and 6% respectively, and the surface strength of 13.7 MPa concrete is increased by 16.7%.

Steel-Reinforced Concrete Floors With The Use Of Bent Steel Profiles

The issues of designing a steel-reinforced concrete floor using bent steel profiles are considered. The steel-reinforced concrete flooring consists of a monolithic reinforced concrete slab arranged on a removable formwork, and steel bent profiles. The removable formwork during the concreting process rests on steel beams without additional mounting posts in the floor span. Steel beams accept the weight of the formwork and concrete during the pouring, working on bending. After concrete strengthening, they mainly work on stretching as part of composite steel-reinforced concrete structure. The article has identified the advantages and disadvantages of steel-reinforced concrete flooring with the use of light steel thin-walled bent profiles. Checking the strength of the beam at the concreting stage and evaluating the load-bearing capacity of the floor after the concrete strength is set confirm the performance of this structure. Using the regulatory methodology for SP 266.1325800.2016, the area of implementation of steel and concrete flooring with CFS beams and the nomenclature of applied steel beams have been established. For practical application of the presented design, it is recommended to conduct experimental and theoretical research and develop engineering methods.

Flexural Behaviour of Unbonded Posttensioned Concrete Beam Strengthened with Aluminium Alloy Plates

Owing to their high corrosion resistance, aluminium alloy (AA) plates bonded with magnesium phosphate cement (MPC) are considered as a viable candidate for reinforcing inshore infrastructures that are subject to severe environmental conditions and vapor atmospheres. Therefore, the aim of this study is the evaluation of the flexural behaviour of simple beams that are strengthened using this technique. Six unbonded posttensioned concrete (UPC) beams with different reinforcement ratios are damaged by static loads and then repaired and strengthened using AA plates. The failures under two-point loading are then investigated. Thereafter, a simplified method is proposed for the evaluation of the flexural strength of a UPC beam strengthened by an AA plate with MPC. The flexural strengths of the six specimens increase by an average of 14%, and the displacement ductility factor decreases by an average of 34.14%. Moreover, the increase and decrease ratios are proportional and inversely proportional to the comprehensive reinforcement index, respectively. The influences of the three main factors on the flexural strength of the AA plate are determined: the increase in the stress of the unbonded tendons, stress at the midspan and slippage at the ends of the AA plate, and increase ratio of the flexural strength. It shows that the AA plates bonded with MPC can be used successfully in concrete strengthening.

Effect of Adding Porcelain and Glass Powder Mixture on Epoxy Properties

In this research, porcelain powder and glass was added by 0.25% (0.15% porcelain powder and 0.1% glass powder) to the epoxy used in the concrete strengthening. The addition improved epoxy properties and reduced the cost. The results showed that the addition of porcelain and glass powder decrease the interaction temperature by 11.37%, epoxy flow by 10.41%, and increase the compressive strength by 7.61%. Upon testing the improved epoxy cubes under the effect of temperatures up to 200ᵒ C compression resistance decreased by 6.36%, while both modulus of rupture and modulus of elasticity improved by (1.03% and 4.11%) respectively. The epoxy was tested and used to strengthen reinforced concrete beams and tests showed good improvement in flexural properties.

Self-Sensing CFRP Fabric for Structural Strengthening and Damage Detection of Reinforced Concrete Structures

This paper presents a concept of a Self-sensing Carbon Fiber Reinforced Polymer (SCFRP) system, which integrates the piezoceramic transducers with the common concrete strengthening materials, CFRP fabric. This integration provides the SCFRP fabric with the ability to monitor the structural health condition when the SCFRP fabric is applied on reinforced concrete structures. In order to validate the feasibility of this system, several three-point bending beam (3PBB) specimens were fabricated and tested before and after the specimens were reinforced with the proposed SCFRP fabric. In addition, the specimens with the low (C25) and high (C40) concrete grades were also experimentally investigated to evaluate the reinforced effectiveness of the SCFRP fabric. Finally, the experimental results demonstrate that the proposed SCFRP fabric can significantly improve the bearing capacity of the concrete structures, and provided the reinforced concrete structures with an ability of self-sensing their health condition.

Strengthening airfield pavements with cement concrete layers

The paper presents original solutions and methodology for determining the thickness of cement concrete strengthening layers for repairing and upgrading existing flexible and rigid airfield pavements. Flow diagrams and nomograms for determining edge stress were developed. These are novel solutions which have not been presented in a similar form before now. After deriving the above relations, a method for the practical utilisation of the resulting monograms depending on the parameters of existing airfield pavement and properties of the cement concrete strengthening layer is presented. Preparing calculation-based charts using the derived equations will markedly shorten the procedure of selecting the thickness of cement concrete strengthening layers for existing flexible airfield pavements that require repair depending on the degree of their wear. Keywords: rigid airfield pavement, flexible airfield pavement, pavement strengthening