Showing papers in "Concrete international in 2003"

Corrosion of highway bridges: economic impact and control methodologies

Abstract: This paper reports on results of research to determine the cost of corrosion with respect to reinforced concrete highway bridges. In 1998, 9% of conventional reinforced concrete bridges and 3% of prestressed concrete bridges in the United States were found to be structurally deficient. The overall area of structurally deficient bridges is 370 million sq ft, with these structural deficiencies largely attributable to corrosion. The annual direct cost of corrosion for highway bridges is estimated to be between $64.3 billion and $10.15 billion. Life-cycle analysis estimates indirect costs due to traffic delays and lost productivity at more than 10 times the direct costs of corrosion. Employing best maintenance practices is estimated to save 45% of the annual corrosion costs of a bridge deck reinforced with black steel. A significant portion of corrosion can be attributed to deicing salts. To avoid corrosion from the chloride, bridge designers should choose reinforcement resistant to corrosion, make the concrete less corrosive at specific chloride levels or prevent chlorides from reaching the steel surface by coating the reinforcement or providing physical barriers at the concrete surface. Surface barriers, cathodic protection and electrochemical chloride removal can reduce corrosion and extend service life for existing bridges. Summaries of costs and resulting life expectancy for these methods are provided. Increased funding and greater awareness of new construction materials and corrosion control methodologies should be utilized to extend bridge life expectancy.

Comparison of Concrete Rheometers

Abstract: This paper describes how fresh concrete is a complex fluid consisting of a suspension of a high volume of water with high volume percentage of particulate solid that has a very wide particle size distribution. The rheological properties of fresh concrete control the flow behavior of the material in mixing, placement, consolidation and finishing. Test methods that measure flow using a single parameter (e.g. slump) cannot properly evaluate the rheological properties of concrete in all uses. The paper describes how the American Concrete Institute (ACI) committee 236A, with the support of the Concrete Research Council and industry, has tested four concrete rheometers that were specifically designed to evaluate rheological properties of concrete materials. The second test series expands the data from the first test series using the same approach of bringing the rheometers together at a common test site and testing the same concrete mixtures simultaneously. All of the rheometers can measure a flow curve for fresh concretes with slumps in the range from 100 mm to 250 mm or non-segregating concretes with slump flows in the range from 300 mm to 800 mm. Each rheometer evaluates yield stress and plastic viscosity by fitting a Bingham model flow curve to measurements of rotation rate and torque for each mix. All of the rheometers gave different absolute values for the Bingham constants of yield stress and plastic viscosity for each mix. But all of the rheometers ranked the mixes in the same order for both yield stress and plastic viscosity.

FRP Materials and Concrete - Research Needs

Abstract: Fiber-reinforced polymer (FRP) composite materials have existed since the 1940s, but it has only been recently that their use in concrete construction has become acceptable. Although the research community has made great progress in identifying and quantifying the characteristics of FRP materials and the behavior of concrete members and systems reinforced or prestressed with FRP materials, there is still a lack of understanding and design guidance that limits the broader implementation of FRP materials in concrete applications. To identify perceived research needs associated with the use of FRP materials in concrete applications, members of the ACI Committee on Fiber Reinforced Polymer Reinforcement were surveyed. The committee represents experts in industry, practitioners, and academia. Three general needs were identified: (1) design and construction guidelines and specifications; (2) standardized material test methods; and (3) data on the durability of FRP materials and FRP reinforced concrete systems. Specific research needs on durability, fire resistance, repair and retrofit, internally reinforced concrete members, prestressed concrete members, constituent materials and processing, FRP properties and test methods, quality assurance and nondestructive evaluation, design considerations and field applications are discussed.

A New Source of Pozzolanic Material

Abstract: Wood ash, a by-product of combustion from boilers at thermal power-generating facilities, has the potential for use in beneficial, environmentally friendly applications. In order to examine potential applications for wood ash in cement-based construction materials, this study investigates the various physical, chemical and microstructural properties of wood ash. Wood fly ash from 12 sources and wood bottom ash from 5 sources were examined. Moisture content, particle size distribution, unit weight, cement pozzolanic activity, water requirement, and autoclave expansion was determined for each source. The samples were analyzed for their total chemical makeup by instrumental neutron activation analysis. Scanning electron microscopy images of the wood ash particles were obtained to understand their microstructure. The source of wood ash was found to have a significant effect on its properties. Many of the wood ash properties were found to be very consistent with a pozzolanic material. Several potential applications of wood ash exist in cement-based materials, including controlled low strength material (CLSM), low and medium strength concrete, cast-concrete products, roller-compacted concrete pavements, road base-course materials and blended cements. Wood ash containing CLSM can also be used as both excavatable and nonexcavatable fill material. Further testing is being conducted on commercial applications of wood ash.

How the water-cement ratio affects concrete strength

Abstract: This paper seeks to determine whether the influence of the water-cement ratio (w/c) on concrete strength arises only from the fact that a part of the mixing water produces voids that weaken the mass of hydrated cement paste, or if there are other factors involved. The paper reviews the literature on the relationship of compressive strength and w/c and concludes that porosity is not a factor at very low values of w/c. It follows then that bonds between the hydrated cement paste must be an influence on strength. The considerations of porosity and of bonds can be combined by appreciating that porosity affects the strength of bonds through the influence of the distance between hydrating surfaces. Thus, bonds appear to be the fundamental factor influencing the relationship between strength and w/c. A study of the relationship between the strength of mortar and the strength of concrete, both materials containing a cement paste with the same w/c, has failed to establish a physical explanation of the available test results. The w/c also is shown to influence the rheological behavior of concrete.

Preventing progressive collapse in concrete buildings

Abstract: To prevent progressive collapse, buildings should be designed and detailed with an adequate level of ductility, redundancy and continuity so that alternative load paths can develop following the loss of an individual member. These characteristics also are desired in seismic design. This paper illustrates the inherent reserve capacity of seismically detailed reinforced concrete (RC) moment-resisting frames that helps make the system resist progressive collapse. A study was conducted on a simple 12-story RC frame building representative of existing construction. The analysis was performed using General Services Administration progressive collapse design criteria and element removal procedures. Each progressive collapse scenario was evaluated using a three-dimensional linear elastic model of the structure. Results showed that seismically designed RC moment-resisting frames do provide a structure with continuity, redundancy and ductility. Both new and existing structures designed and detailed with such a system already have an inherent ability to better resist progressive collapse. Progressive collapse of RC buildings can be mitigated through proper structural system selection without substantially increasing project cost.

Composite pile: a successful drive

Abstract: Fiber-reinforced polymer (FRP) composites can be used with concrete in hybrid construction, where concrete provides the bulk mass, and the FRP serves as a load-carrying partner and protects the concrete from environmental deterioration. Concrete-filled FRP tubes are hybrid systems that can provide an alternative to conventional concrete piles. Based on their investigation, the authors suggest some requirements for FRP tubes, including: sufficient hoop strength to provide confinement and shear resistance, sufficient axial strength to replace the internal concrete reinforcement, chemical inertness to the alkalis in the concrete core, lack of voids to prevent moisture intrusion, ultraviolet protection for the portion of the tube that will be above ground, rough surface in friction piles and bond with concrete to provide composite action and shear transfer. A field study was conducted to compare the drivability of composite piles to prestressed concrete piles. A steel pile cap was used for the composite pile to ensure that the FRP tube and the concrete would absorb the driving energy together. The hammer drove the composite pile to a depth of 6.8 m and the prestressed pile to a depth of 7.3 m with no signs of damage to either pile. A detailed analysis indicated that the driving stresses of the composite piles were comparable to those seen in the prestressed pile. Blow counts for the composite piles were found to vary somewhat proportionally to the depth of pile in soil, in contrast with the softening observed in the case of the prestressed pile. The difference is attributed to the geometry and surface characteristics of the two types of piles. The end bearing area and the friction surface of the composite pile are both about 75% of the respective values of the prestressed pile.

HVFA Concrete—An Industry Perspective

Abstract: Although high-volume fly ash (HVFA) concrete can lead to significant cost savings and offers environmental benefits, the industry has been reluctant to accept fly ash contents at high proportions because of perceptions about its effects on constructability and performance. This paper addresses some issues and concerns about HVFA concrete, including early strength gain, initial setting time, bleeding and curing and air entrainment. Fly ash content of 40-50% of cementitious material can be used for structural elements that require no finishing, such as columns, walls, beams, precast elements with a compressive strength of 750 psi (5.2 Mpa) by 14-16 h, drilled piers, mud mats and some foundations. For precast and prestressed elements with a compressive strength of 3000 to 6000 psi by 16 h that do not require finishing, a fly ash content of 20-30% is recommended. For structural elements that need finishing, such as slabs-on-ground, foundations, concrete pavements, tilt-up walls, suspended slabs, slabs on metal deck and toppings, a fly ash content of 40-50% is acceptable if the structure will be broom finished. If these elements will be trowel finished, a fly ash content of 25-50% is recommended. In order to more effectively use HVFA concrete, engineers should reexamine strength requirements to specify only the strength essential for a structural element at the appropriate age and intended service. Concrete mixtures with varying percentages of fly ash should be regularly tested by material suppliers and concrete producers to give engineers more information for specifying HVFA concrete.

Forces of hydration that can cause havoc in concrete

Abstract: Volume changes caused by hydration of water soluble salts and relatively insoluble anhydrous compounds can deteriorate concrete. This article describes the mechanisms that create the forces of deterioration and provides examples of distress caused by the phenomenon. Instances where these forces have been harnessed for useful purposes are also described. To avoid damage to concrete due to free lime and periclase, it is recommended that portland cements and hydraulic cements be used that meet maximum autoclave expansion requirements of 0.80%. Steel-making slag should not be incorporated in concrete, and concrete should not be contaminated with materials that contain free lime, periclase and potentially expansive salts. To mitigate damage due to laumontite-leonhardite, do not use aggregates that contain them.

Landmark Series: Further Studies on the Effect of Entrained Air on Strength and Durability of Concrete with Various Sizes of Aggregates

Abstract: PREVIOUS TESTS USING A NATURAL SAND AND A CRUSHED SILICEOUS GRAVEL INDICATED THAT, FOR CONCRETES OF CONSTANT CEMENT CONTENT AND CONSISTENCY (VARYING WATER-CEMENT RATIO), ADEQUATE RESISTANCE TO FREEZING AND THAWING OF AIR-DRIED CONCRETES WAS SECURED WHEN THE AIR CONTENT OF THE MORTAR FRACTION WAS 9 PLUS OR MINUS 1 PERCENT, REGARDLESS OF THE MAXIMUM SIZE OF AGGREGATE USED. THE TESTS REPORTED HEREIN ARE FOR CONCRETES MADE WITH CEMENTS FROM THE SAME SOURCE AS THE INITIAL TESTS AND THE SAME NATURAL SAND. HOWEVER, THE COARSE AGGREGATE USED WAS A CRUSHED LIMESTONE WITH PARTICLE SHAPE AND TEXTURE DIFFERENT FROM THOSE OF THE GRAVEL PREVIOUSLY USED. THREE CEMENT CONTENTS WERE USED AT A CONSTANT SLUMP OF 5 TO 6 INCHES: 4.0, 5.5 AND 7.0 SACKS PER CUBIC YARD OF CONCRETE. THE MAXIMUM SIZES OF AGGREGATE USED WERE 3/8-IN., 3/4-IN. AND 1 1/2-IN. FOR EACH COMBINATION OF CEMENT CONTENT AND MAXIMUM SIZE OF AGGREGATE, FIVE CONCRETES COVERING A FAIRLY WIDE RANGE OF AIR CONTENTS WERE PREPARED. THE RESULTS OF FREEZING AND THAWING TESTS OF THESE CONCRETES CONFIRMED THE RESULTS OF THE EARLIER TESTS. ADEQUATE RESISTANCE TO FREEZING AND THAWING WAS OBTAINED WHEN THE AIR CONTENT OF THE MORTAR FRACTION WAS IN THE RANGE OF 9 PLUS OR MINUS 1 PER CENT. THE REPORT ALSO INCLUDES INFORMATION ON THE EFFECT OF ENTRAINED AIR ON STRENGTH, RESISTANCE TO SALT SCALING, VOLUME CHANGE AND ABSORPTION OF THESE CONCRETES. /AUTHOR/

Strut-and-tie model for deep beam design

Abstract: Truss models have long been used as tools for the analysis and design of reinforced concrete members. In the past 20 years, the use of the truss analogy to analyze and design regions of structural members, particularly those in which the assumptions of plane sections remaining after loading is clearly inadequate, has been the subject of considerable research. In these works, limit analysis is used to evaluate the strength of the compression strut and tension tie members of the truss, as well as the nodes connecting them. These truss models are thus typically referred to as strut-and-tie models. Although truss or strut-and-tie models have long served as the basis of shear design methods for beams with web reinforcement, some design standards have incorporated formal provisions for the use of strut-and-tie models. Because these provisions typically include rules for estimating the size and strength of all the components in truss models, design using the strut-and-tie approach is often tedious and time consuming. This effectively compromises one of the pillars of the truss analogy: simplicity. This paper aims to show that, in many cases, design of deep beams using the strut-and-tie method can be substantially simplified using simple rules that have passed the test of time.

Sprayed-fiber-reinforced composite materials for infrastructure rehabilitation

Abstract: This paper reports on a pilot study to evaluate the use of sprayed-fiber-reinforced polymer (SFRP) composite materials in structural rehabilitation. The procedure, quality and mechanical properties of SFRP composite materials were investigated. The test program involved standard concrete flexural specimens tested under third-point loading conditions. Results showed that SFRP enhances the load-carrying, toughness and displacement capacity of plain concrete beams in flexure. The presence of chopped fibers did not have a significant effect on the load capacity of the specimens, but did enhance the deformation capacity of the beams. SFRP was also found to have an apparent reduced in-place strength compared to tensile coupon tests. Other results showed that SFRP is well suited for direct application to moderately deteriorated concrete surfaces and that it provides good mechanical bond to concrete surfaces. The skill of the person applying the SFRP, epoxy temperature, application orientation and type of fiber were observed to affect the quality of the SFRP product.

Code provisions for high-strength concrete: an international perspective

Abstract: This article compares some of the provisions from five different codes of practice--the American Concrete Institute Building Code Requirements for Structural Concrete, the Comite Euro-International du Beton Model Code, the European Committee for Standardization for Design of Concrete Structures, the Canadian Standards Association for Design of Concrete Structures and the Standards Association of New Zealand Concrete Design Standard--for the structural design of elements made with high strength concrete. While codes from different countries have similar objectives, they sometimes have significant differences in their requirements for the design of high-strength concrete members. These differences often reflect the region/country's prior state of the art and tradition. Provisions concerning compressive strength limits, load and resistance factors, specified and characteristic strengths, modulus of elasticity, concrete tensile strength, minimum reinforcement for flexure, stress distributions for determining the nominal resistances under flexure and axial loads, and column confinement for seismic design are compared.

Post-Tensioned Masonry Around the World

Abstract: Unreinforced masonry with low axial loads, as typically found in modern construction, exhibit a poor cracking behavior and low strength for large lateral loads and deformation. This is especially true in seismic regions. The application of a moderate amount of axial load using post-tensioning can help overcome these disadvantages by enhancing the strength, cracking behavior and ductility of masonry walls. Post-tensioning also provides effective connections between walls and diaphragms to avoid failure of the joints. Post-tensioning is most frequently applied vertically to masonry walls exceeding 10 to 12 ft. Anchorage at either end of the tendons is preferably placed in concrete elements. Case studies highlighting the possible uses of post-tensioning in masonry construction, including one example of post-tensioned masonry for a pedestrian bridge deck, are included.

Fabric-formed concrete members

Abstract: This article provides an introduction to the technique of flexible fabric formwork for concrete and describes several strategies currently being developed. The efficient production of variable section shapes is made possible by the development of inexpensive, strong structural textiles. Computers are permitting the analysis of increasingly complex and efficient structural geometries. Fabric formwork offers several significant advantages: it is lightweight and low-cost; it offers improved finish, density and strength; and it is well suited to the production of high-efficiency structural members. Opportunities for future research and construction projects using the method are discussed. Full-scale, fabric-formed columns, walls and foundations are being built in North America and Japan, but the technique also holds potential promise for developing countries, especially those that lack wood. Full-scale tests of many formwork designs need to be performed, along with structural tests of fabric-formed variable-section beams and slabs. Software is also needed to support flexible formwork design and the structural design of fabric-cast variable-section members.

Cost-effective scc for deep foundations

Abstract: This study investigates the possibility of producing economically competitive self-consolidating concrete (SCC) for the construction of drilled shaft piles and caissons. The authors optimized cost-effective, high-volume cement replacement SCC that does not compromise the early-age strength of SCC. Four aspects were considered in the mixture proportioning: (1) reducing the coarse aggregate content and its maximum particle size to minimize interparticle friction; (2) incorporating high volume of one or more low-cost mineral admixtures to increase the volume of the cement paste and improve its particle size distribution, therefore enhancing paste deformability and concrete stability; (3) introducing a high-range water-reducing admixture (HRWRA) to achieve the required workability of SCC without increasing the water content and therefore maintaining the desired strength and ductility of concrete; and (4) introducing a viscosity-modifying admixture in some cases to offset any reduction in concrete cohesiveness caused by the addition of the HRWRA and enhance resistance to segregation. The workability, compressive strength and cost effectiveness of the various SCC mixtures were investigated. Results indicated that an economically competitive SCC can be achieved by replacing up to 50% of ordinary portland cement with mineral admixtures such as fly ash, ground-granulated blast furnace slag and limestone filler. Incorporating such admixtures in binary, ternary or quaternary blends can enhance the rheological behavior of SCC and decrease its material cost. Excellent compressive strength values can also be attained using these admixtures.

Bridge deck cover depth specifications

Abstract: Concrete cover is the first line of defense in preventing the corrosion of reinforcing steel. This article presents the results of two bridge deck cover depth surveys in order to determine the most desirable method for specifying reinforcing steel cover depths. One method specifies a bridge deck cover depth of 2.5 in with tolerance limits of -0 and +0.5, and includes a supplemental pay item to the contractor for placing an additional 0.5 in of concrete. Both data sets in the two bridge deck cover depth surveys have the same cover depth limits of 2.5 to 3.0 in. One data set includes the supplemental pay item in the project specification, while the other set is for bridge decks built without the inclusion of the supplemental pay item. Statistics on cover depth and time for initiation of corrosion are given. The mean time for initiation of corrosion is 40-41 years for both data sets. However, 13% of the sample decks in the data set where the supplemental pay item was not included had an estimated time to corrosion initiation of less than 30 years. In comparison, none of the decks in the sample with the supplemental pay item had an estimated time of corrosion of less than 30 years. These results show that the supplemental pay item for an additional 0.5 in of concrete has prevented the construction of bridge decks with less than desirable cover depths and thus, shorter service lives.

Full-scale test of prestressed double-tee beam

Abstract: The Bridge Street Bridge in Southfield, Michigan, is the most recent carbon fiber-reinforced polymer (CFRP) prestressed concrete bridge in the United States, and the first to use CFRP tendons, carbon fiber composite cable (CFCC) strands and CFRP sheets. Due to the lack of existing design standards for FRP prestressed concrete bridges, the design and construction approach was validated by testing a full-scale double-tee (DT) beam to failure. This study describes the experimental investigation of the DT test beam, including critical major structural parameters such as concrete strains, deflections, forces in the post-tensioning strands at the service load, cracking load, ultimate load, and the type and pattern of failure experience at the ultimate load. Results showed that the combined internal and external prestressing induced the desired compressive strains in the cross section, which balanced the tensile strains induced by the applied load to prevent service load cracking in the beam. The ultimate flexural capacity and the cracking of the DT beam were determined to be about 3.4 and 1.2 times the service moment, respectively. In addition, the tested flexural strength was about 1.6 times that of the calculated capacity. The beam webs experienced significant cracking before the failure load. Crushing of the concrete topping, followed by the rupture of the internal prestressing tendons, initiated the failure of the DT beam. However, none of the external unbonded CFCC post-tensioning strands ruptured. These results provided the design team with enough information to proceed with the development of the design approach and construction documents for the bridge.

Quantifying Condition Indicators for Concrete Structures

Abstract: This paper reports on a probabilistic model of concrete quality indicators to optimize inspection and maintenance planning of a concrete structure. This model is unique in that it takes into account physical, statistical and model uncertainties in the condition assessment. This approach can be used for planning activities, such as determining the acceptance criteria based on the owner's choice of the risk of misinterpretations (accepted error) or figuring the optimal time to perform non-destructive testing in the inspection routine. In turn, this method allows for rational assessment of data and quantifies the effect of accepted error, allowing quantitative guidelines for the assessment of similar structures in similar environments. The approach is illustrated with an example of highway bridge columns exposed to deicing salt. Half-cell potential mapping is investigated as an inspection method for the indication of initiated corrosion and visual inspection is used as an indicator of reduction in the stirrup's cross-sectional area. Inspection and maintenance planning was optimized to minimize the expected total service life cost. Results show that half-cell potential mapping is applicable as a quantitative condition indicator for the example. However, for many other classes, half-cell potential mapping is a poor indicator of reinforcement corrosion. Overall findings suggest that the decision model that considers localized deterioration should only be applied in situations where the deterioration is indeed localized or for smaller structures. For larger structures, classes each consisting of several stochastically independent elements may be identified and thus the decision model for distributed deterioration should be used.

Guidelines for the design of post-tensioned floors

Abstract: This article provides a set of guidelines to assist the design engineer in the post-tensioning design of floors for typical buildings and parking structures. For any given member geometry, support conditions and loading, the design of a post-tensioned member depends on three parameters that need to be established: the average precompression (prestressing force), the percentage of load to balance (uplift due to tendon drape) and the tendon profile (shape and drape). Anchor locations and additional considerations such as cover for fire resistance, tendon layout, tendon stressing and selection of nonprestressed reinforcing bar size are also addressed. The guidelines reflect industry practice for economical design. Based on observed performance of structures built to these guidelines, the guidelines lead to safe structures with good in-service performance.

Producing and evaluating portland cement-based rapid strength concrete: New technology for full depth repair

Abstract: This paper describes a new technology that allows normal-portland-cement based concrete to reach rapid early-flexural strength and thus reduce closure time when making pavement repairs. The system uses polycarboxylate high-range water-reducing admixtures, coupled with a nonchloride accelerator and a patented hydration control additive to achieve high strength very quickly. The experimental program described in this paper began in the laboratory and continued concurrently in the field to validate lab test results. Several chemical admixtures were selected for the initial laboratory tests. The primary factors evaluated were the hydration control admixture dosage, the polycarboxylate formulation, the nonchloride accelerator chemistry and the accelerator dosages. Results showed that most of the test mixtures reached the targeted flexural strength of 400 psi at 5h after mixing began. High early strength did not compromise later-age strength development. Higher air contents were shown to affect both early-age compressive and flexural strength. However, a significant early-age strength was obtained when sufficient air is entrained. The field test from interstate repair work showed that the concrete developed the required flexural strength at 400 psi at 4 h after placement. Specific procedures for producing the concrete are recommended based on the field and laboratory results. The key to producing this concrete is shown to be a relatively low water-cementitious material ratio coupled with proper admixture selections based on the materials employed and the application involved.

Can we determine the age of cracks by measuring carbonation? part 1

Abstract: Measurement of depth of carbonation has potential use in estimating the time since the occurrence of a crack. This paper reviews carbonation and its measurement in general. Understanding the phenomena involved is vital to proper testing and to the interpretation of observations during testing. The simplest test for distinguishing carbonated and uncarbonated concrete is to spray phenolphthalein lightly onto a freshly exposed surface. Since there is no standard for this test, this article provides advice on the conducting the test and proper preparation of the test surface. Under steady conditions, the depth of carbonation increases in proportion to the square root of time of exposure. A second part of this article will deal specifically with carbonation around cracks and gives a definitive answer on whether the age of crack can be determined by measuring carbonation.

Self-consolidating concrete solves challenging placement problems

Abstract: This article describes how self-consolidating concrete (SCC) was used to fill 100-foot high steel composite columns at a new airport terminal in Toronto, Ontario The concrete had to be pumped vertically from the bottom of the column The concrete for the job had to be homogenous, with little tendency to bleed and segregate Appropriate mix proportions were developed to achieve 30 MPa at 28 days strength and a slump flow between 650 and 750 mm Sufficient time of plasticity was required to ensure ease of pumping A test placement was conducted before the SCC was placed in the remaining 179 columns Water-reducing admixtures were used to achieve and maintain the specified slump flow throughout the pumping process This unique use of SCC provided a cost-efficient solution for a difficult project

Uhpc anchors for post-tensioning

Abstract: This article describes the development of a new anchor for post-tensioning applications involving carbon fiber-reinforced polymer tendons. A mechanical gripping, split-wedge anchor method was chosen. The anchor was developed using ultra-high-performance concrete (UHPC) with very high compressive strength, enhanced durability and fracture toughness. Twelve tests, incorporating 14 anchors, examined both static and dynamic performances of the anchor. Static tests resulted in an average anchor capacity of 99.7 kN, with a coefficient of variation of 2%. Dynamic load testing exhibited excellent fatigue performance for the UHPC anchor. The UHPC anchor will first be used in post-tensioned masonry diaphragm walls.

Producing and Evaluating Portland Cement-Based Rapid Strength Concrete

Abstract: This paper describes a new technology that allows normal-portland-cement based concrete to reach rapid early-flexural strength and thus reduce closure time when making pavement repairs The system uses polycarboxylate high-range water-reducing admixtures, coupled with a nonchloride accelerator and a patented hydration control additive to achieve high strength very quickly The experimental program described in this paper began in the laboratory and continued concurrently in the field to validate lab test results Several chemical admixtures were selected for the initial laboratory tests The primary factors evaluated were the hydration control admixture dosage, the polycarboxylate formulation, the nonchloride accelerator chemistry and the accelerator dosages Results showed that most of the test mixtures reached the targeted flexural strength of 400 psi at 5h after mixing began High early strength did not compromise later-age strength development Higher air contents were shown to affect both early-age compressive and flexural strength However, a significant early-age strength was obtained when sufficient air is entrained The field test from interstate repair work showed that the concrete developed the required flexural strength at 400 psi at 4 h after placement Specific procedures for producing the concrete are recommended based on the field and laboratory results The key to producing this concrete is shown to be a relatively low water-cementitious material ratio coupled with proper admixture selections based on the materials employed and the application involved