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Properties Of Concrete

Critical Chloride Content in Reinforced Concrete: A Review

Unmanned surface vehicles: An overview of developments and challenges

Chloride threshold level for corrosion of steel in concrete

This paper presents the results from an experimental program and an analytical assessment of the influence of addition of fibers on mechanical properties of concrete. Models derived based on the regression analysis of 60 test data for various mechanical properties of steel fiber-reinforced concrete have been presented. The various strength properties studied are cube and cylinder compres- sive strength, split tensile strength, modulus of rupture and postcracking performance, modulus of elasticity, Poisson's ratio, and strain corresponding to peak compressive stress. The variables considered are grade of concrete, namely, normal strength 35 MPa, moderately high strength 65 MPa, and high-strength concrete 85 MPa, and the volume fraction of the fiber Vf=0.0, 0.5, 1.0, and 1.5%. The strength of steel fiber-reinforced concrete predicted using the proposed models have been compared with the test data from the present study and with various other test data reported in the literature. The proposed model predicted the test data quite accurately. The study indicates that the fiber matrix interaction contributes significantly to enhancement of mechanical properties caused by the introduction of fibers, which is at variance with both existing models and formulations based on the law of mixtures. 85 MPa with various fiber dosages Vf=0, 0.5, 1.0, and 1.5%. An empirical relationship for various mechanical properties of SFRC has been proposed. The proposed model attempts to bring out the significance of fiber matrix interaction in all the strength properties. This study reports the experimental results of the strength properties of SFRC, namely, cube and cylinder compressive strength, split tensile strength, modulus of rupture, modulus of elasticity, Poisson's ratio, and strain corresponding to peak com- pressive stress. Empirical relationships were developed for vari- ous strength properties based on the regression analysis of the 60 test data. It is expected that these proposed models would be helpful in assessing the strength properties of fiber-reinforced concrete based on the matrix strength and fiber-RI.

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Mechanical Properties of Steel Fiber-Reinforced Concrete

The Center for Robot-Assisted Search and Rescue (CRASAR®) deployed a customized AEOS man-portable unmanned surface vehicle and two commercially available underwater vehicles (the autonomous YSI EcoMapper and the tethered VideoRay) for inspection of the Rollover Pass bridge in the Bolivar peninsula of Texas in the aftermath of Hurricane Ike. A preliminary domain analysis with the vehicles identified key tasks in subsurface bridge inspection (mapping of the debris field and inspecting the bridge footings for scour), control challenges (navigation under loss of GPS, underwater obstacle avoidance, and stable positioning in high currents without GPS), possible improvements to human-robot interaction (having additional display units so that mission specialists can view and operate on imagery independently of the operator control unit, incorporating 2-way audio to allow operator and field personnel to communicate while launching or recovering the vehicle, and increased state sensing for reliability), and discussed the cooperative use of surface, underwater, and aerial vehicles. The article posits seven milestones in the development of a fully functional UMV for bridge inspection: standardize mission payloads, add health monitoring, improve teleoperation through better human-robot interaction, add 3D obstacle avoidance, improve station-keeping, handle large data sets, and support cooperative sensing.

Robot-Assisted Bridge Inspection

Controlled low-strength material (CLSM) is a self-compacting, flowable, low-strength, cementitious material used primarily as backfill, void fill, and utility bedding in lieu of conventional compacted fill. Potential advantages of CLSM include decreased labor requirements, faster construction speed, and potentially lower in-place cost. When considering CLSM as a construction material, 2 of the most important properties include flowability and compressive strength. The flowability of CLSM can directly impact productivity and human resource requirements for placing the material. Lower flowability may require more resources. In addition, compressive strength values are required as an indicator for performance and long-term excavatability. Minimum strength requirements are necessary for performance criteria, and maximum strength requirements are necessary for long-term excavation. This research investigated the effects of material properties on the water demand necessary to obtain minimum flowability values and a range of compressive strength values for CLSM. Three types of aggregate, 3 types of fly ash, and 1 Type I cement were used in this study. A total of 31 mixtures were developed and tested. The use of different aggregate types and sources was found to be the most significant factor affecting water demand in this investigation. Water-cement ratio, aggregate sources, and fly ash type were influencing variables on the compressive strength of CLSM. Formulas were developed to predict the compressive strength development of CLSM for the materials used in this research program.

Effects of Constituent Materials and Quantities on Water Demand and Compressive Strength of Controlled Low-Strength Material

Corrosion performance of conventional (ASTM A615) and low-alloy (ASTM A706) reinforcing bars embedded in concrete and exposed to chloride environments

High-strength concrete (HSC) is widely used in prestressed concrete bridges (PCBs). Current design guidelines for PCB structures such as the AASHTO LRFD specifications, however, were developed based on mechanical properties of normal-strength concrete (NSC). As a first step toward evaluating applicability of current AASHTO design provisions for HSC prestressed bridge members, statistical parameters for the mechanical properties of plant-produced HSC were determined. In addition, prediction equations relating mechanical properties with the compressive strength were evaluated. HSC samples were collected in the field from precasters in Texas and tested in the lab at different ages for compressive strength, modulus of rupture, splitting tensile strength, and modulus of elasticity. Statistical analyses were conducted to determine the probability distribution, bias factors (actual mean-to-specified design ratios), and coefficients of variation for each mechanical property. It was found that for each mechanical property, the mean values are not significantly different among the considered factors (precaster, age, specified strength class) or combination of these factors, regardless of specified design compressive strength. Overall, 28-day bias factors (mean-to-nominal ratios) decrease with increases in specified design compressive strength due to relative uniformity of mixture proportions provided for the specified strength range. Still, the 28-day bias factors for compressive strength are higher than those used to calibrate AASHTO LRFD specifications. With few exceptions, the coefficients of variation were uniform for each mechanical property. In addition, the coefficients of variation for the compressive strength and splitting tensile strength of HSC in this study are lower than those for NSC used in the development of the AASHTO LRFD specifications.

David Trejo

Papers

Robot-Assisted Bridge Inspection

Effects of Constituent Materials and Quantities on Water Demand and Compressive Strength of Controlled Low-Strength Material

Corrosion performance of conventional (ASTM A615) and low-alloy (ASTM A706) reinforcing bars embedded in concrete and exposed to chloride environments

Mechanical Properties of High-Strength Concrete for Prestressed Members

Accelerated Chloride Threshold Testing: Part I-ASTM A 615 and A 706 Reinforcement