The research presented in this dissertation focuses on the material characterization of ultrahigh performance fiber reinforced concrete (UHP-FRC) at both the microscopic and macroscopic scales. The macroscopic mechanical properties of this material are highly related to the orientation of the steel fibers distributed within the matrix. However, the fiber orientation distribution has been confirmed to be anisotropic based on the flow-casting process. The orientation factor and probability density function (PDF) of the crossing fiber (fibers crossing a cutting plane) orientation was obtained based on theoretical derivations and numerical simulations with respect to different levels of anisotropy and cut planes oriented arbitrarily in space. The level of anisotropy can be calibrated based on image analysis on cut sections from hardened UHP-FRC prisms. Simplified equations provide a framework to predict the mechanical properties based on a single fiber-matrix interaction rule selected from existing theoretical models. Along with the investigation of the impacts from different curing methods and available post-cracking models, a versatile parameterized uniaxial stress-strain constitutive model was developed and calibrated. The constitutive model was implemented in a finite element analysis software program, and the program was utilized in the preliminary design of moveable bridge deck panels made of passively reinforced UHP-FRC. This deck system was among the several alternatives to replace the problematic steel grid decks currently in use. Based on experimental investigations of the deck panels, failure occurred largely in shear rather than flexure during bending tests. However, this shear failure is not abrupt and usually involves large deformation, large sectional rotation, and wide shear cracks before loss of load-carrying capacity. This particular shear failure mode observed was further investigated numerically and experimentally. Three-dimensional FEM models with the ability to reflect the interaction between rebar and concrete were created in a commercial FEM software to investigate the load transfer mechanism before and after bond failure. Small-scale passively reinforced prisms were tested to verify the conclusions drawn from simulation results. In an effort to improve the original design, several shear-strengthened deck panels were tested and evaluated for effectiveness. Finally, methods and equations to predict the ultimate shear capacity iii were calibrated. A two-dimensional frame element based complete moveable bridge finite element model was built for observation of bridge system performance. The model contained the option to substitute any available deck system based on a subset of pre-calibrated parameters specific to each deck type. These alternative deck systems include an aluminum bridge deck system and a glass fiber reinforced plastic (GFRP) deck system. All three alternatives and the original steel grid deck system were evaluated based on the global responses of the moveable bridge, and the advantages and disadvantages of adopting the UHP-FRC deck system are quantified.

No description available.

yes / ACI Committee 544’s repeated drop-weight impact test for concrete is often criticized for large variations within the results. This paper identifies the sources of these large variations and accordingly suggests modifications to the ACI test. The proposed modifications were evaluated and compared to the current ACI test by conducting impact resistance tests on 40 specimens from two batches of polypropylene fiber-reinforced concrete (PPFRC). The results obtained from both methods were statistically analyzed and compared. The variations in the results were investigated within the same batch and between different batches of concrete. The impact resistance of PPFRC specimens tested with the current ACI test exhibited large coefficients of variation (COV) of 58.6% and 50.2% for the first-crack and the ultimate impact resistance, respectively. The corresponding COV for PPFRC specimens tested according to the modified technique were 39.4% and 35.2%, indicating that the reliability of the results was significantly improved. It has been shown that, using the current ACI test, the minimum number of replications needed per each concrete mixture to obtain an error below 10% was 41 compared to 20 specimens for the modified test. Although such a large number of specimens is not good enough for practical and economical reasons, the reduction presents a good step on the development of a standard impact test.

Adjacent voided slab bridges (AVSB) are economical systems for short spans. They provide the advantages of having low clearances due to their small section depths, accelerated construction times, and high torsional stiffness. The current longitudinal connection detail, a partial depth grouted shear key, has been known to fail in many of these bridges. The failure leads to reflective cracking in the wearing surface which allows chloride laden water to seep down through the joint, where it corrodes the reinforcement and prestressing strand. Ultimately, the failed keys lead to costly repairs and bridge replacements sooner than their proposed lifespan. This research project aimed to develop a more durable longitudinal connection detail by using sub-assemblages to test five alternate connections. The objective was to find a connection that abated all cracking in the shear key, thus removing the need for transverse post-tensioning. The tested connections employed alternate connection shapes and two different mix designs of fiber reinforced high strength concretes. The results showed that each tested connection outperformed the current detail. The findings of this research indicate that the longitudinal connection detail of adjacent member voided slab bridges should be modified. The modified version should be a blockout with lap splice connection detail utilizing a nonproprietary fiber reinforced high strength concrete. / Master of Science

It has been known that the nucleation and growth of cracks and defects dominate the fatigue damage process in brittle or quasi-brittle materials, such as woven fabric composites and concrete. The behaviors of these materials under multiaxial tensile or compression fatigue loading conditions are quite complex, necessitating a unified approach based on principles of mechanics and thermodynamics that offers good predictive capabilities while maintaining simplicity for robust engineering calculations. A unified approach has been proposed in this dissertation to simulate the change of mechanical properties of the woven fabric composite and steel fiber reinforced concrete under uniaxial and biaxial fatigue loading. The boundary surface theory is used to describe the effect of biaxial fatigue loading. A fourth-order response tensor is used to reflect the high directionality of the damage development, and a second-order response tensor is used to describe the evolution of inelastic deformation due to damage. A direction function is used to capture the strength anisotropic property of the woven fabric composite. The comparisons between model prediction results and experimental data show the good prediction capability of models proposed in this dissertation.

No description available.

This master thesis summarizes the current knowledge regarding the design and properties of glass fiber reinforced concrete products. It also deals with the design of a new concrete recipe for Dako spol. s.r.o company. There is verified effect of changes in input materials in real conditions the company to increase tensile bending strength above 20 MPa.In particular, verification of the use of building chemistry like superplasticizing additives, polymer-cement matrix or a change type or dose of glass fiber.

Adequate interfacial bond performance of Bonded Concrete Overlay (BCO) systems requires novel integration of material mixture design, compatibility model development, and interfacial bond design. This entails the use of the right materials, on the right substrate, in the right way, in order to secure the best possible composite behaviour. The overall composite performance of BCOs depends largely on achieving the right proportion of blend for the overlay material. The use of mixture experiments provides a flexible, easy, and quick way of optimizing multi-component materials of this nature. This study describes the use of optimization techniques within the concept of material mixture experiments for proportioning and designing the material constituents of a Bonded Roller Compacted Fibre Reinforced Polymer Modified Concrete (BRCFRPMC). By constraining the range of variability of the constituents, a feasible design space was created with 13 experimental points treated based on the required structural and elastic properties of the overlay. The optimum consistency-time for full consolidation and composite behaviour with the substrate ordinary Portland cement concrete (OPCC) was established between 34.05 and 34.87 seconds, while the resulting apparent maximum density achieves between 97.11% - 98.03% of the theoretical air-free density. In addition, compressive strength response at early and matured ages of 3 and 28 days were satisfied at 100% desirability. The elastic modulus response at age 3 showed 0% desirability, but attains about 99.96% of the target response by 28 days. The verification experiments conducted on each response property shows that positive correlations exist between the measured responses and the predicted values from the optimization analysis. Also, the bond capability of the optimum designed overlay material was evaluated using both tensile and shear bond strengths parameters. The overall assessment results showed that the overlay material exhibits good bonding with the substrate OPCC and would be able to withstand substantial stresses where sufficient surface texture is provided for aggregates interlocking. Other material properties included in the evaluation process of the overlay material included its tensile strength, coefficient of thermal expansion, and drying shrinkage. Stresses in the overlay, substrate, and at the interface were assessed analytically under various differential movement related conditions. Though the interface and the overlay material exhibited sufficient strength against thermal and shrinkage cracking, the theoretical shrinkage cracking in the overlay was predicted at 6.92MPa when fully restrained axially. Further, for effective fracture process description of the interface, experimentally determined parameters in shear and tension were coupled in Mixed-Mode Finite Element Analysis using differential edge deformation model between the overlay and the underlay. The results indicated that delamination in partial fracture process varied from that of complete fracture process, influenced distinctly and largely by the magnitude of the applied load. Other influencing factors in the analyses included the elastic mismatched properties, initial edge defect size, and the plane of loading. Lastly, analytical solution to the FEA problem was implemented using the proposed Modified Eigenvalue Buckling Analysis (MEBA). The result indicated that the proposed analytical method simulates and compares well with the FEA result. The proposed method also provided a good technique for predicting the Mixed-Mode Buckling failure Mode-Shape of the overlay.

Thesis (PhD (Civil Engineering))--University of Stellenbosch, 2007. / ECC (Engineered Cement-based Composites) is a type of HPC (High Performance Concrete) that was engineered to overcome the weaknesses of ordinary concrete. It shows high ductility as it can resist the full tensile load at a strain of more than 3 %. This superior response is achieved with multiple cracking under tensile loading which has a pseudo strain hardening phenomenon as result. The purpose of the research project reported in this dissertation is to investigate and characterise the time-dependant behaviour of ECC and create a constitutive model to numerically simulate the static and time-dependant behaviour of ECC. To investigate the time-dependant behaviour experimentally, rate and creep tests were done on the meso- and macro-level while rate tests were done on the structurallevel. The meso-level was represented by the pull-out testing of fibres embedded in the cement-based matrix and direct tensile tests were done for the macro-level. Flexural tests on thin beams were done to simulate the structural-level. Strong time-dependant behaviour was found on all three these levels. On the meso-level, the most prominent finding is that the failure mechanism can change with a change of strain rate, i.e. fibre pull-out at a low pull-out rate, while with a high pullout rate, fibre rupture can occur. Even though the strength of a tensile specimen on the macro-level showed a dependence on the strain rate, the ductility remained constant over four orders of magnitude of the strain rate. On the structural-level, however, a reduction of the flexural ductility was found with an increase of the ...

Thesis (MScEng (Civil Engineering)--University of Stellenbosch, 2006. / Some experiments utilizing the shear capacity of Engineered Cement-based Composites (ECC) have suggested that elimination of shear reinforcement is feasible when the concrete matrix is replaced by ECC. However, actual application and more rigorous cost analysis are prevented by the fact that the shear stress and strain properties of ECC have not yet been characterized as accurately as the tensile properties. This study focuses on the investigation of the shear property of ECC. The study starts with a survey and comparison of existing shear tests for composite materials. The Iosipescu shear test concept is chosen as the most objective method for ECC, and subsequently, modified for specific application on ECC by simple analytical design and finite element refinement. The modified Iosipescu shear test method is applied on, four types of ECC specimens with different fibre content (0%, 1%, 2%, 2.5% by volume), which have been cast in specially designed moulds and cured in laboratory conditions. Three phases of shear measurements are used to check the shear test appropriateness and study the shear mechanical properties of ECC. The failure mode is verified in the first phase, detailed measurement of the shear strain and shear stress is performed and recorded in the second phase, and in the third phase more information about the ductility of diagonal cracking is obtained by measurement of the tensile principal deformation. By also conducting direct tensile tests on specimens of the exact same mix, information of both uniaxial tension and shear behaviour is available, from which elastic and shear moduli, as well as Poisson’s ratio of ECC are computed. A first step toward application of this knowledge of the shear behaviour of ECC is taken by studying the response of shear-dominated beams and beam-columns of reinforced concrete and reinforced concrete combined with ECC as the outer crusts. These beams were prepared and tested by other members of the research group of the Division for Structural Engineering of the University of Stellenbosch. It is shown that ECC can indeed successfully replace shear reinforcing steel, due to its shear capacity.