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

Effect of strain softening on the ultimate strength and stability of flexible frames.

The principal role of any structural connection is to transfer forces safely between the various components meeting at that joint. Therefore, it is important for these connections to provide adequate structural strength to resist the loads and possess the necessary ductility to deform as the structure resists the loads. Local buckling or distortion of cross-section due to the complexities and irregularities in geometry of many types of connections of found to be a source of softening in the moment-rotation behavior of some kinds of connections and has an effect on the maximum load-carrying capacity of steel structures. In this study, a computer program is developed for the analysis of flexibly jointed frames. The connections are represented by nonlinear spring elements at the ends of members. An elastic-plastic hinge plane frame analysis including the effect of nonlinear connection behavior is presented to predict the ultimate load-carrying capacity of steel frames with sufficient accuracy. Members between plastic hinges are assumed to behave elastically. The nonlinear moment-rotation behavior of the connection is represented by a four parameters Richard model. The main objective of this study is to investigate the effect of connections with a strain softening behavior on the ultimate strength and stability of flexible frames. Further studies include the effect of connection flexibility on the drift of multi-story frames. The result of the analysis shows that the drift in multi-story frames can be reduced by increasing the stiffness of the connections used in the structure. Numerical studies of frames made using the developed computer program are presented. Observations regarding the effects of flexible connections on the strength and deflection of steel framed structures are discussed. The proposed analyses considering flexible joints using Richard model to represent the connection behavior were found to be simple and accurate

Experimental Evaluation of Drying Shrinkage and Mechanical Properties of Repair Materials for Concrete Structures

The potentially aggressive environments in some parts of Saudi Arabia have resulted in premature deterioration of many concrete structures during their service life. To achieve more effective and long lasting repair materials, it is essential that the properties of the repair materials and the substrate are compatible. This study aims at evaluating the mechanical properties of selected classes of repair materials that are commonly used in repair application within the Kingdom. A total of 114 specimens were cast to investigate some of the important properties of nine widely used local repair materials available in the market. The properties evaluated in this study are: drying shrinkage, compressive strength and modulus of elasticity. Out of each of the selected repair materials, six specimens for shrinkage and six specimens for compressive strength and modulus of elasticity measurements were considered in the study. Additional specimens made from cement paste were used as control samples for the study. Results of the present study show that all repair materials must be checked experimentally to confirm the properties given by the supplier before their use in any field application. The study also recommends that the selection of suitable repair material should be based on the type of application, as application changes properties requirement changes. For example, for one application compressive strength requirement may be more critical, while in another application shrinkage may be of great concern. Keywords: Repairing materials, Cementitious, Drying shrinkage, Compressive strength, Modulus of elasticit

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

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

Shear strength of functionally graded self-compacting concrete deep beams reinforced with steel and GFRP bars

Glass fiber-reinforced polymer (GFRP) bars are emerging as a potential replacement for steel rebars due to their vulnerability to corrosion. However, the shear behavior of GFRP bars is not well established, especially in functionally graded self-compacting concrete (SCC) deep beams reinforced with hybrid rebars (GFRP and steel). This article experimentally explores the behavior of functionally graded high-strength SCC deep beams having a hybrid of steel and GFRP bars as tension reinforcement. A total of fourteen deep beams were prepared with varying reinforcement ratios and steel fiber volume fractions. There were three groups of deep beams: (i) plain SCC (i.e., no fibers) beams, (ii) fiber-reinforced SCC (FRSCC) beams having 0.6 % and 1.2 % steel fibers, and (iii) functionally graded deep beams. The functional grading was achieved by casting beams in two layers, with the first layer of lower two-thirds depth having steel fibers and the second layer without fibers. The beams were shear deficient and tested in flexure. The shear resistance of functionally graded deep beams was compared with beams having fibers in full depth and without fibers. The test results reveal the significance of the hybrid system of rebars, which is found to effectively improve the structural capacity of concrete beams and increase the load required to initiate cracking. In addition, the mixing of fibers in concrete enhanced the deep beam shear capacity by 15–23 % for 0.6 % fibers and 37–39 % for 1.2 % fibers. The increase in the shear resistance of concrete deep beams was not influenced by the use of hybrid rebars compared to using GFRP bars only. A model is developed for assessing the shear resistance of functionally graded fiber-reinforced concrete deep beams by incorporating the dowel action of hybrid longitudinal reinforcing bars. The study indicates that the dowel action provided by GFRP bars is comparable to the steel bars of the same area

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

Shear behavior of self-consolidating concrete deep beams reinforced with hybrid of steel and GFRP bars

This paper experimentally investigates the dowel action contribution of longitudinal reinforcement, a hybrid of steel and GFRP bars (usually adopted for avoiding corrosion of steel bars), in concrete deep beams for different reinforcement schemes. The self-consolidating concrete without and with steel fibers (0.9 % and 1.2 % by volume) was used. Sixteen simply supported deep beams of 140 × 300 (depth) × 1500 mm were tested under the two-point loads. A model is developed to predict the shear capacity of deep beams without web reinforcement, taking into consideration the dowel action contribution of longitudinal reinforcement, which is a hybrid of steel and GFRP rebars. The results showed a significant dowel action contribution of steel as well as GFRP rebars to beam shear strength. However, the use of a hybrid system of steel and GFRP bars caused a reduction in the dowel action of steel bars due to their combined action