Effect of some biotic factors on microbially-induced calcite precipitation in cement mortar

Sporosarcina pasteurii, a common soil bacterium has been tested for microbial treatment of cement mortar. The present study also seeks to investigate the effects of growth medium, bacterial concentration and different buffers concerning the preparation of bacterial suspensions on the compressive strength of cement mortar. Two growth media, six different suspensions and two bacterial concentrations were used in the study. The influence of growth medium on calcification efficiency of S. pasteurii was insignificant. Significant improvement in the compressive as well as the tensile strength of cement mortar was observed. Microbial mineral precipitation visualized by Scanning Electron Microscopy (SEM) shows fibrous material that increased the strength of cement mortar. Formation of thin strands of fillers observed through SEM micrographs improves the pore structure, impermeability and thus the compressive as well as the tensile strengths of the cement mortar. The type of substrate and its molarity have a significant influence on the strength of cement mortar

Flexural Performance of RC Beams Repaired with Commercial Repair Materials

Different types of cementitious repair materials are commercially available in the local market. Almost all repair material suppliers claim that their products are most suitable for concrete repair under different environmental and loading conditions. This necessitates the need to check all aspects of the repair materials which include their behavior when used in structural elements. The objective of this research was to investigate the performance of the most commonly used cementitious repair materials when used to repair structural elements. This was achieved through the evaluation of the flexural performance of 24 RC beams repaired using nine selected types of the most commonly used repair materials (supplied by three leading suppliers in the country). The results were compared with two identical beams repaired with concrete and also with two identical beams cast with concrete monolithically (no repair). The results showed that the repair materials subjected to tensile stresses had no significant contribution (to beam response) compared to normal concrete. However, the influence of the repair materials was much better when used to repair structural parts subjected to compressive stresses. Keywords: RC beams, Repair materials, Flexural performanc

Rehabilitation of the Infrastructure Using Composite Materials: Overview and Applications

The volume of the infrastructure that needs upgrading, strengthening and/or repair is growing worldwide. The traditional techniques of rehabilitation are faced with challenges from new materials and methods that offer convenience in application and lesser degree of financial constraints to the owner. The new advances made with fiber reinforced polymer (FRP) composites, because of their many advantages over steel and other conventional materials, have provided engineers with stimulus in circumventing the difficulties associated with the traditional techniques of rehabilitation process. Although the applicability of the new materials and techniques are verified by more than ten years of field applications and a bulk of experimental data, many engineers, owners, architects and contractors still have hesitation in taking the full advantage of these materials. Some of the major reasons behind this hesitation are: the absence of code of practice, standards, guidelines for design and detailing, and the lack of clear understanding of the structural performance of the composite structure under short- and long-term loads. Although, it might be argued that the material cost of FRP is about 5 to 10 times than that of steel, the total cost of retrofitting with FRP materials in general is more economical as compared to steel. This is true because in a retrofitting operation, material cost is only a fraction of the total retrofitting cost, the remainder being the application, labor and maintenance costs. Moreover, ease of installing, handling, storage, transporting and the life cycle cost benefits of FRP could lead to a great saving in the overall cost that may exceed the difference in the material cost. This paper provides an overview of the engineering properties of FRP as a repair and retrofit material for infrastructure applications. It also presents a state-of-the-art information of research and development undertaken in the area of using advanced composite materials for rehabilitation of infrastructure components

Performance of Concentrically Loaded RC Wall-like Columns Upgraded with Innovative Hybrid NSM/CFRP System

In RC (reinforced concrete) frame structures, wall-like columns are laid within the space occupied by masonry walls to maximize usable space and thus minimize the column projections into the usable area. These columns often require strengthening owing to various reasons, including increasing the number of stories, changes in building usage, and others. The use of a hybrid system comprising NSM (near-surface mounted) steel rebars combined with CFRP (carbon-fiber reinforced polymer) laminates may be considered a sound technique for strengthening such wall-like building columns. The prime aim of this study is to devise an efficient scheme using a hybrid NSM/CFRP system to strengthen existing RC wall-like columns. Six half-scale RC wall-like columns were prepared and tested under monotonic concentric axial compression. Two columns were unstrengthened to serve as control specimens (CW1 and CW2), and four specimens were strengthened using four different schemes (SW1, SW2, SW3, and SW4). As favored by architects, all strengthening schemes were designed so that the dimensions of the column cross-section were not increased. The effects of strengthening schemes on the enhancement of axial capacity, energy dissipated, and stiffness were evaluated to find the most efficient scheme. Among the four studied schemes, using vertical continuous NSM rebars in combination with the wrapping of the three CFRP layers onto the exterior column surface (in specimen SW2) was the most efficient as it enhanced the ultimate load capacity by 80%. Three-dimensional FE (finite element) analysis was also conducted to predict the response of test specimens. The test results matched well with the FE outputs, which justified the accuracy of the used constitutive models for concrete, steel rebars, and CFRP sheets

Performance of FRP-Upgraded RC One-Way Ribbed Slabs with an Opening in Flexure Zone

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings

Influence of Treatment Methods of Recycled Concrete Aggregate on Behavior of High Strength Concrete

Worldwide the concrete industry has started embracing the utilization of recycled concrete aggregates (RCAs) resulting from demolition and construction waste as full or partial substituents in the production of high-strength concrete (HSC) due to their economic and environmental benefits. Several parameters were experimentally investigated in this study. The first parameter analyzed the effect of replacing varying percentages of coarse aggregate with recycled aggregate. The second parameter examined the influence of two aggregate sizes (10 and 20 mm). The third parameter was intended for investigating the influence of three different RCA treatment methods utilizing sodium silicate immersion, cement slurry, and the Los Angeles (LA) abrasion simulation. The test results generally indicated degradation in the engineering properties of concrete produced using untreated RCA compared to the control. The degree of reduction increased as the replacement percentage was increased regardless of the aggregate size. The reduction in compressive strength appeared to have a more pronounced effect in comparison to the splitting tensile strength. The use of treated RCA improved concrete slump by 15–35%. This also caused enhancement in the engineering properties, especially for the LA abrasion mechanical treatment, which was very promising for both aggregate sizes. In comparison with the untreated RCA, the relative enhancement in water absorption was up to 76%, whereas splitting tensile and compressive strengths increased by 3–50% and 5–60%, respectively

Prediction of Ballistic Limit of Strengthened Reinforced Concrete Slabs Using Quasi-Static Punching Test

The formulas available in the literature for predicting the projectile impact response of reinforced concrete (RC) targets are generally developed based on the results of impact tests. Recently, however, in order to avoid performing involved and challenging projectile impact tests, the impact response of RC targets was predicted using the quasi-static punching response of RC slabs. In this paper, the concept is extended to concrete slabs strengthened with textile-reinforced mortar (TRM) or carbon fiber-reinforced polymer (CFRP) sheets externally bonded to the concrete surface. In 16 groups, 96 slabs of 600 × 600 × 90 mm size were cast and tested under quasi-static and impact loads. The slabs were reinforced with two types of reinforcement: ϕ8@100 mm and ϕ4@25 mm. The singly and doubly reinforced concrete slabs with rebar spacing of 100 mm were strengthened using externally bonded CFRP and TRM on the back side of the slab specimens. Two mixes of concrete, representing normal and high-strength concretes, were used. The results of the present study reveal that the CFRP and TRM strengthening of RC slabs enhanced the energy absorption in punching by 57–130% and 20–59%, respectively. The use of WWM in singly and doubly reinforced slabs also resulted in a 30–42% and 41–63% increase in energy absorption in punching, respectively. An earlier proposed model was modified to incorporate the influence of strengthening (CFRP and TRM) in the estimation of the projectile perforation energy of the strengthened RC slabs with the help of energy absorbed in their quasi-static punching. This perforation energy was then employed for predicting the ballistic limit of CFRP- and TRM-strengthened slabs. The predictions show good agreement with the experimentally observed ballistic limits

Behavior of FRP-Strengthened RC Beams with Large Rectangular Web Openings in Flexure Zones: Experimental and Numerical Study

Abstract This paper aims to investigate the behavior of fiber reinforced polymer (FRP) strengthened reinforced concrete (RC) beams containing large rectangular web openings in the flexure zone. Studied parameters were type of loading, opening size and strengthening scheme. Seven RC beams categorized into two different groups were tested. In the first group, two unstrengthened beams (one solid without opening and one with large rectangular web opening in the pure flexure zone) were tested under four-point bending. In the second group, five beams were tested under center-point loading. They comprised of one reference solid beam and four beams with large rectangular web opening in the maximum-moment region. Out of the four beams with openings, two specimens were unstrengthened and the other two were strengthened with two different FRP schemes. A numerical study was also conducted and the results of analysis were validated with experiments. The calibrated analysis was then used for some useful parametric studies in which the effect of different parameters was investigated