International Concrete Abstracts Portal

An investigation was carried out on basalt fiber-reinforced concrete (BFRC) produced using various dosages of basalt fibers. The concrete mixture was designed with a target strength of 35 MPa (5075 psi), which is a typical strength for floor slabs and similar applications in which fiber reinforcement is often used. The concrete was tested for slump and air content in the fresh condition and for compressive strength, splitting tensile strength, flexural strength, and toughness in the hardened condition. Using these tests, the behavior of the BFRC was investigated and compared to fiber-reinforced concretes produced using similar dosages of polypropylene polyethylene synthetic fibers and crimped steel fibers. The basalt fibers were found to generally increase tensile and flexural strength (modulus of rupture), but were found to have very little effect on compressive strength and post-cracking behavior, and inspection found that the fibers had ruptured upon macrocracking.

Cast-in-drilled-hole (CIDH) piles are often constructed to depths that are inaccessible, and internal vibration is not performed over the length of the pile. Because of this, the likelihood of voids occurring increases. Many state highway agencies use inspection pipes to detect if voids are present along the length of the pile. High reinforcement densities and concrete void detection inspection pipes can congest CIDH piles. Although concrete void detection and reinforcement spacing are critical to ensuring adequate CIDH pile structural performance, eliminating concrete voids can also ensure expected performance. This research will assess the influence of coarse aggregate (CA) type and mixture proportions on concrete workability for CIDH pile applications. Results indicate that identifying an optimal paste volume-to-aggregate void ratio (PV/AV) can be used to proportion flowing concrete (FC) mixtures with adequate slump flow and stability. Concrete containing rounded CA achieved higher slump flow values than concrete with crushed CA at the same paste volume. However, increasing PV/AV also decreased stability. Stability was increased by increasing the FA-to-CA ratio (FA/CA).

A pilot-scale field investigation was conducted through which: 1) a refined ultra-high-performance concrete (UHPC) mixture was prepared in a ready mixed concrete plant; 2) a large reinforced UHPC block was constructed through placement, consolidation, and finishing of UHPC; and 3) a commonly available concrete curing (insulating) blanket was applied for field thermal curing of the UHPC block using the exothermic heat of hydration of the cementitious binder in UHPC. Monitoring of the reinforced UHPC block temperature over time confirmed the development of a reasonably uniform temperature and a viable temperature time history, which suited thermal curing of UHPC without any heat input. In-place nondestructive inspection of the reinforced UHPC structure pointed at timely setting and strength development, leading to achievement of ultra-high-performance status. Specimens were cored from the large reinforced concrete block and subjected to laboratory testing. The experimental results indicated that the field thermal curing was more effective than the laboratory thermal curing considered in the project, and that the pilot-scale production of the UHPC mixture produced compressive strengths approaching 170 MPa (24.7 ksi).

An inspection scheme is presented for detecting global damage in reinforced concrete structures. In-house software is used to generate quantitative damage assessment metrics. Temporal sensor data captured during a bridge inspection can be post-processed to analyze stability and produce strength representations. Structural weak points can be visually located, and the developed tool can decrease inspection time and increase its accuracy. This risk monitoring provides objective guidance on a structure’s current health as compared to any previous condition, currently limiting applications to periodic inspection. As verification, a laboratory-built reinforced concrete bridge is analyzed by comparing an as-built baseline to four damage cases with artificial pier softening. Signal processing, modal decomposition, and health quantification produced visual plots for 12 metrics indicating both damage severity and location. The developed methodology is employed to demonstrate that flexibility absolute difference, damage location vector, and modal flexibility index most accurately located pier connection damage.

This paper discusses the measured out-of-plane thermomechanical behavior of two full-scale reinforced concrete (RC) bearing wall test structures subjected to fire loading. A special skid-mounted movable gas furnace was designed and constructed for heating of one face of each wall specimen over half of the wall height through the ASTM E119 standard fire time-temperature curve. Each specimen formed one face of the furnace (that is, the specimen was not enclosed by the furnace), allowing easier visual inspections and monitoring of out-of-plane behavior on the unexposed surfaces, and the application of gravity and lateral loads on the structure. In addition to an array of discrete thermocouples, strain gauges, and displacement/rotation sensors, full-field deformation and temperature response of selected surfaces of the test specimens were captured using digital image correlation (DIC) and infrared thermography. Both test specimens were fixed at the base and free to displace vertically and rotate at the top. A constant axial load representing tributary gravity loading was applied at the top. In the out-of-plane lateral direction, the top of the first specimen was restrained, while the top of the second specimen was allowed to displace under increasing temperatures and a step-wise increasing external lateral load. The test results show that RC bearing walls are robust structures that can withstand long periods of extreme fire exposure. The out-of-plane lateral strength and stability under gravity loads, however, can be compromised due to the unsymmetrical deterioration of the concrete and reinforcing steel over the wall thickness, as well as the development of significant out-of-plane shear forces due to restrained thermal bowing.

The state-of-the-art of fiber-reinforced polymer (FRP) composite stay-in-place (SIP) structural form systems for bridge decks is presented in this paper. This technique involves constructing a concrete deck whereby prefabricated FRP components act as both the permanent formwork and the bottom flexural reinforcement. The advantages and limitations of the technology are presented, along with the current progress of experimental and analytical investigations. Extensive laboratory investigation is presented covering numerous aspects of the system, including strength, fatigue, and environmental performance. A variety of system configurations are discussed. Examples of field applications are presented, along with evaluations of cost effectiveness and inspection considerations. The result of these investigations show that FRP SIP formwork systems can be both constructible and meet applicable code requirements for strength and serviceability. Preliminary cost assessments suggest that increases in material costs can be partially offset by savings in labor during installation. Finally, future research needs are identified.

When load-rating the large number of diagonally cracked reinforced concrete (RC) deck-girder bridges constructed during the 1950s, the modern AASHTO LRFD check of flexural tension reinforcement anchorage can limit member ratings. The rating check compares the tensile demand in the reinforcing bar to the available tensile force at the section of interest. Among other parameters, the tensile demand is controlled by the diagonal crack angle at the section. The crack angles noted in inspections are generally flatter than those in the provisions and engineers are uncertain as to the inputs. The available tensile force in the flexural steel depends on the embedded reinforcing length; however, information is limited regarding bond stress developed with larger-diameter bars for full-size specimens. This research produced new flexural anchorage data in diagonally cracked girders that will help bridge engineers evaluate older concrete bridges. The results showed that the available bond strengths are higher than presently prescribed in ACI 318.

This paper presents an experimental investigation for detecting defects in concrete structures using so-called “smart aggregates.” The smart aggregates are small cylinders with piezoelectric patches inside that can be embedded in concrete structures and used as both actuators and sensors. Specimens with different types of defects such as notch, hole, and inclusion were used in this study. To evaluate the effectiveness of the smart aggregates for detecting real cracks in concrete structures, three-point bending tests were carried out on two reinforced concrete beams. The test results indicate that not only the passive defects (notch, hole, or inclusion) but also the real cracks in reinforced concrete structures can be detected by the smart aggregates. Sensitivities of different parameters (time-of-flight, energy content of the signals, wavelet packet decomposition-based damage index) for various defects were also investigated.

An accelerated corrosion study to assess the feasibility of acoustic emission (AE) for the detection of active corrosion in prestressing strand is described. Concrete prisms with an embedded steel strand were corroded by supplying a constant potential between the strand and a copper plate while the specimens were immersed in a 3% NaCl solution. Corrosion was detected using the half-cell potential (HCP), steel section loss, and visual inspection, and the results were compared to AE data. The location of active corrosion was determined experimentally based on the characteristic wave speed. An intensity analysis approach was used to plot the relative significance of the corrosion damage and a classification chart is presented. Results indicate that AE is a useful, nonintrusive technique for the detection and quantification of corrosion damage and may be developed as a structural prognostic tool for maintenance prioritization.

This paper describes the monitoring of axial strains and curvatures in the slabs and columns of a flat-plate post-tensioned concrete parking deck. Shrinkage-compensating concrete (SCC) was used for the parking deck in lieu of pour strips to speed up construction. The 59 vibrating-wire strain meters were installed during construction in the spring and summer of 2008 and have hourly recorded strains and temperatures until present. Measured axial strains in the slab clearly show expansion due to the SCC, elastic shortening due to post-tensioning, contraction due to creep and shrinkage, and thermal expansion and contraction due to daily and seasonal temperature variations. Preliminary analyses indicate that the SCC experienced significantly less creep and shrinkage than that predicted by design equations for normal concrete. Visual inspections of the slab revealed essentially no cracks due to slab contraction (caused by creep, shrinkage, and temperature change).