American Concrete Institute Committee Research Articles

Prediction of compressive strength and evaluation of different theoretical standards and proposed models of brick columns confined with FRP, FRCM, or SRG system

The strength capacity of confined masonry column is one of the topics that need to be studied. In this study, the efficiency of using different types of advanced composite (non-corrosive materials) such as fiber reinforced polymer (FRP), fiber reinforced cementitious matrix (FRCM), or steel reinforced grout (SRG) in confining masonry columns is investigated. A wide range of experimental database of masonry column specimens has been collected from the results that available in scientific literatures. Different theoretical standards and proposed models that used to predict the capacity of masonry columns confined with FRP and FRCM are evaluated based on collected experimental database. Since there is no standard code or specific proposed model for SRG system, the confined capacity of this system is predicted and evaluated using the FRCM proposed models. The justification of using these models is that both FRCM and SRG systems have the same concept of using inorganic material as a paste material. An index named “equivalent fiber reinforcement index (EFRI)” is proposed to capture the key factors that control the behavior of the confined masonry columns with different advanced composite. This index is used as reference parameter for the purpose of the comparison between different strengthening systems. As a result, all types of advanced composite presented a significant increase in ultimate capacity. Also, the behavior of the masonry columns was significantly dependent on the type of fabric used. Different modes of failure were reported, including crushing of masonry block, as well as a deboning of FRP from the masonry substrate and deboning or slippage of fabric within inorganic paste matrix. Compared with other models and standards, the American Concrete Institute Committee 440 (ACI 440) and American Concrete Institute Committee 549 (ACI 549) shows very good predictions for the confined capacity of masonry columns strengthened by FRP and FRCM or SRG respectively.

The Effect of Bottom Ash Ball-Milling Time on Properties of Controlled Low-Strength Material Using Multi-Component Coal-Based Solid Wastes

As the conventional disposal method for industrial by-products and wastes, landfills can cause environmental pollution and huge economic costs. However, some secondary materials can be effectively used to develop novel underground filling materials. Controlled low-strength material (CLSM) is a highly flowable, controllable, and low-strength filling material. The rational use of coal industry by-products to prepare CLSM is significant in reducing environmental pollution and value-added disposal of solid waste. In this work, five different by-products of the coal industry (bottom ash (BA), fly ash, desulfurized gypsum, gasification slag, and coal gangue) and cement were used as mixtures to prepare multi-component coal industry solid waste-based CLSM. The microstructure and phase composition of the obtained samples were analyzed by scanning electron microscopy and X-ray diffraction. In addition, the particle size/fineness of samples was also measured. The changes in fresh and hardened properties of CLSM were studied using BA after ball milling for 20 min (BAI group) and 45 min (BAII group) that replaced fly ash with four mass ratios (10 wt%, 30 wt%, 50 wt%, and 70 wt%). The results showed that the CLSM mixtures satisfied the limits and requirements of the American Concrete Institute Committee 229 for CLSM. Improving the mass ratio of BA to fly ash and the ball-milling time of the BA significantly reduced the flowability and the bleeding of the CLSM; the flowability was still in the high flowability category, the lowest bleeding BAI70 (i.e., the content of BA in the BAI group was 70 wt%) and BAII70 (i.e., the content of BA in the BAII group was 70 wt%) decreased by 48% and 64%, respectively. Furthermore, the 3 d compressive strengths of BAI70 and BAII70 were increased by 48% and 93%, respectively, compared with the group without BA, which was significantly favorable, whereas the 28 d compressive strength did not change significantly. Moreover, the removability modulus of CLSM was calculated, which was greater than 1, indicating that CLSM was suitable for structural backfilling that requires a certain strength. This study provides a basis for the large-scale utilization of coal industry solid waste in the construction industry and underground coal mine filling.

Expected compressive strength in precast, prestressed concrete design: Review and discussion of regional practice

Accurate estimates of expected concrete compres­sive strength are critical for designers to predict the deformational behavior of precast, prestressed concrete elements such as camber, deflections, and prestress losses. To explore the difference between specified and expected concrete compressive strength for Alabama bridge girders, a compressive strength data set repre­senting 1887 girder production events was collected. The average measured concrete compressive strength for Alabama girders was 33% greater than the specified strength at prestress transfer and 59% greater than the specified 28-day strength. Available empirical strength prediction methods derived for other U.S. regions did not accurately represent the Alabama data. The most promising candidates for prediction methodologies for expected compressive strength were models based on guidance from the American Concrete Institute Committee 214 for the prediction of expected strength at prestress transfer and models based on concrete strength-growth modeling to predict 28-day strength.

Statistical evaluation of the mechanical properties of high-volume class F fly ash concretes

High-Volume Fly Ash (HVFA) concretes are seen by many as a feasible solution for sustainable, low embodied carbon construction. At the moment, fly ash is classified as a waste by-product, primarily of thermal power stations. In this paper the authors experimentally and statistically investigated the effects of mix-design factors on the mechanical properties of high-volume class F fly ash concretes. A total of 240 and 32 samples were produced and tested in the laboratory to measure compressive strength and Young’s modulus respectively. Applicability of the CEB–FIP (Comite Euro-international du Béton – Fédération Internationale de la Précontrainte) and ACI (American Concrete Institute) Building Model Code (Thomas, 2010; ACI Committee 209, 1982) [1,2] to the experimentally-derived mechanical property data for HVFA concretes was established. Furthermore, using multiple linear regression analysis, Mean Squared Residuals (MSRs) were obtained to determine whether a weight- or volume-based mix proportion is better to predict the mechanical properties of HVFA concrete. The significance levels of the design factors, which indicate how significantly the factors affect the HVFA concrete’s mechanical properties, were determined using analysis of variance (ANOVA) tests. The results show that a weight-based mix proportion is a slightly better predictor of mechanical properties than volume-based one. The significance level of fly ash substitution rate was higher than that of w/b ratio initially but reduced over time.

Modeling and analysis of the shear capacity of adhesive anchors post-installed into uncracked concrete

This paper reports the results of an analytical study to predict the edge breakout shear capacity of single adhesive anchors post-installed into uncracked hardened concrete. For this purpose, an experimental database for the adhesive anchors compiled by the ACI Committee 355 was obtained and utilized to construct training and test sets so as to derive the closed-form solution by means of gene expression programming (GEP). The independent variables used for development of the prediction model were anchor diameter, type of anchor, edge distance, embedment depth, clear clearance of the anchor, type of chemical adhesive, method of injection of the chemical, and compressive strength of the concrete. The generated prediction model yielded correlation coefficients of 0.98 and 0.92 for training and testing data sets, respectively. Moreover, the performance of the proposed model was compared with the existing models proposed by American Concrete Institute (ACI) and Prestressed/Precast Concrete Institute (PCI). The analyses showed that the proposed GEP model provided much more accurate estimation of the observed values as compared to the other models.

Effectiveness of externally bonded CFRP strips for strengthening flanged beams under torsion: An experimental study

All over the world, fiber reinforced polymer (FRP) is currently being used for strengthening concrete elements, thus improving the building sustainability. The most recent report by the American Concrete Institute Committee 440 suggested that any proposed anchorage system should be heavily scrutinized before field implementation [4]. A comprehensive literature review was conducted, which showed that anchored U-jacket strips and un-anchored extended U-jacket strips were never examined for the case of RC flanged beams under significant torsion. The objective of this study is to investigate the behavior of FRP externally strengthened flanged beams subjected to torsion. Eleven beams were tested under significant torsion. Both the anchored U-jacket and the extended U-jacket strips were found to be more effective strengthening techniques compared to the un-anchored U-jacket strips and as effective as the fully wrapped strips. Using externally bonded FRP strips enhanced the torsional behavior of the flanged beams; however, the level of enhancement depended mainly on the effectiveness of the implemented strengthening technique.

Bond Strength of Lap-Spliced GFRP Bars in Concrete Beams

In this paper, the bond strength of lap-spliced glass fiber–reinforced polymer (GFRP) bars in concrete beams is experimentally investigated. Thirteen beam specimens were manufactured for laboratory experiments. The parameter of transverse reinforcement along the splice length was selected as the main variable for the beam specimens. Other variables were surface properties of GFRP bars, bar diameter, and concrete compressive strength. Test results show that the effect of transverse reinforcement on bond strength between GFRP bars and concrete depends on the surface properties of reinforcing bars. The experimental results obtained in the present study and the results reported in the literature are compared with the current design equation provided by the American Concrete Institute (ACI) Committee 440 guidelines. The equation of ACI Committee 440 for evaluating the bond strength of GFRP bars underestimates the bond strength of spliced GFRP bars confined with large amounts of transverse reinforcement. For cases of small values of transverse reinforcement and splices without transverse reinforcement, the equation of ACI Committee 440 is unconservative and overestimates the bond strength. In this paper, an equation for predicting the bond strength of GFRP bars is also proposed on the basis of test results and the Monte Carlo simulation method.

Non-destructive analysis of chlorine in fly ash cement concrete

Preventive measures against reinforcement corrosion in concrete require increasing concrete density to prevent the diffusion of chloride ions to the steel surface. Pozzolanic materials, such as fly ash (FA), silica fume (SF), and blast furnace slag (BFS) are added to concrete to increase its density. Monitoring the chloride concentration in concrete is required to assess the chances of reinforcement corrosion. In this study, FA was added to Portland cement concrete to increase its density. Prompt gamma neutron activation analysis (PGNAA) technique was utilized to analyze the concentration of chlorine in concrete. The chlorine concentration in the FA cement concrete was evaluated by determining the yield of 1.16, 1.95, 6.11, 6.62, 7.41, 7.79, and 8.58 MeV gamma-rays of chlorine from the FA concrete specimen containing 0.4–3.5 wt% chlorine. An excellent agreement was noted between the experimental yield of the prompt gamma-rays and the calculated yield obtained through the Monte Carlo simulations. The Minimum Detectable Concentration (MDC) of chlorine in FA cement concrete was also calculated. The best value of MDC limit of chlorine in the FA cement concrete was found to be 0.022±0.007 and 0.038±0.017 wt% for 1.16 and 6.11 MeV prompt gamma-rays, respectively. Within the statistical uncertainty, the lower bound of MDC meets the maximum permissible limit of 0.03 wt% of chlorine in concrete set by American Concrete Institute Committee 318.

In-Situ Load Testing: A Theoretical Procedure to Design a Diagnostic Cyclic Load Test on a Reinforced Concrete Two-Way Slab Floor System

The objective of this paper is to showcase to an engineer who is considering performing a diagnostic cyclic load test a theoretical procedure for determining the patch load, which when applied to a two-way reinforced concrete (RC) slab floor system would generate internal forces at critical locations equal to those resulting from the uniformly distributed load. This procedure should also help the practitioner to define a representative model of the structure and to update the magnitude of the target load at the end of each loading and unloading cycle by means of a real-time evaluation of boundary conditions and slab stiffness. The routine to design a cyclic load test is described theoretically first and then validated with the results of a load test on a concrete two-way RC slab floor system. Introduction The current role of testing within structural engineering has gained increasing importance, as it can now be applied to every phase of the structure’s life because of innovative materials and new design approaches. By focusing on either the preliminary testing of a new structure or the necessary control checks prior to assessing the strength of an existing one, in-situ load testing can determine the real behavior of the structure under the existing loading conditions. Accordingly, researchers can have an overall, accurate understanding of the mechanical properties of the structural members. In the United States of America, the current American Concrete Institute (ACI) 318 Building Code [1] provides requirements for load testing of concrete structures. ACI Committee 437 [2] proposes a diagnostic cyclic load (DCL) testing procedure consisting of the application of patch loads in a quasi-static way to the structural member according to loading and unloading cycles. Patch load magnitude and distribution shall simulate the uniformly distributed load defined in the ACI 318 Building Code. The DCL protocol [3,4] defines three acceptance criteria that can be easily computed, in real time, for any structural member by simply checking its behavior under the test load (see Fig. 1 for necessary notation). Repeatability and Permanency represent the behavior of the structure during two identical load cycles; Deviation from linearity represents the measure of the nonlinear behavior of a member being tested. Repeatability = 100 95 B B max r A B max r % % Δ − Δ × ≥ Δ − Δ ; (1) Permanency = 100 10 B r B max % % Δ × ≤ Δ ; (2)

Laboratory Evaluation of Alternative Dowel Bars for Use in Portland Cement Concrete Pavement Construction

Dowel bars are a useful tool for transferring loads from one highway concrete slab to another across joints. Although dowels are used to increase load transfer capabilities across joints, they introduce problems, including stress concentrations and corrosion. Most dowel bars have circular cross sections. The regions of stress concentration for circular dowels are at the top and bottom of the cross section. However, alternative materials and shapes may perform better. Study results showed that elliptically shaped dowels reduced bearing stresses at the dowel–concrete interface. Much research has been conducted at Iowa State University and nationally to study parameter changes and performance of dowels. Parameters including dowel material, dowel shape, joint width, and dowel spacing have been used to evaluate bearing stress performance. Laboratory testing, field testing, and finite element analysis have all been performed to study these parameters. Six highway dowel types representing a variety of material and shape parameters were studied at Iowa State University. All dowels were found adequate to transfer normal highway loads. The deflections measured for all dowels were well within the recommended maximum deflection to ensure rider comfort. The calculations and evaluation of six dowel types showed that none of the specimens failed (dowel yield or concrete failure) before the American Concrete Institute Committee 325 allowable stress was achieved. All six dowels could transfer loads of at least 5,000 lb without exceeding the allowable stresses. Some of the significant findings from this most recent study of dowel parameters are addressed.

Time-Dependent Behavior of a Concrete Integral Abutment Bridge

Time-dependent behavior of an integral abutment bridge near Rochester, Minnesota, was investigated from the beginning of construction through 7 years of service by using field data collected from more than 150 instruments installed in the bridge during construction. Long-term bridge shortening was observed from the readings of horizontal extensometers installed behind the abutments. Measured pile curvatures steadily increased with time. To understand this unexpected bridge behavior better, a time-dependent numerical study using the creep and shrinkage models from American Concrete Institute Committee 209 was conducted. The results obtained in this research indicate that concrete creep and shrinkage had a significant effect on the behavior of the concrete integral abutment bridge over the course of the 7-year study.

Design code development for fibre‐reinforced polymer structures and repairs

AbstractThis paper presents the issues and solutions in developing design codes and standards for the use of fibre‐reinforced polymer (FRP)‐reinforced concrete structures. First, the codes for new construction, referring mainly to the Japan Society of Civil Engineers (JSCE) Recommendations for Design and Construction of Concrete Structures using CFRM (Continuous Fibre Reinforcing Materials), the Canadian Highway Bridge Design Code (CHBDC), and the American Concrete Institute (ACI) Committee 440 recommendations are outlined. Methods discussed are: structural analysis; determination of design values; examination of flexural and shear capacity; precautions to ensure ductility or deformability; and calculations of deformation and development length. Similarly, design codes developed for strengthening of concrete structures with FRP, namely the recommendations by the JSCE, ACI Committee 440, and the fib code are compared and discussed with respect to the ways in which FRP may contribute to improvement of the performance of structures in flexure, shear and ductility. Test methods for different material properties of FRP and the bond of FRP to concrete are also presented, with reference to the JSCE recommendations.

Testing Reinforced Concrete Structures for Watertightnes

The American Concrete Institute Committee 350, Environmental Engineering Concrete Structures, recognized a need for standardized criteria as well as a standardized method of testing reinforced concrete structures for watertightness. AWWA's Committee 400, Waterproofing, was also interested in documenting the state‐of‐the‐art of watertightness testing and criteria for reinforced concrete tanks. A joint subcommittee was subsequently formed to prepare a report containing recommendations on watertightness for reinforced concrete containment structures. This article presents the findings of the joint report.

Precision of Flexural Strength and Toughness Parameters for Steel Fiber Reinforced Concrete

Abstract The variability of parameters used to define the toughness of fiber reinforced concrete under static flexural loading is examined to establish the precision statistics needed for ASTM standards dealing with toughness measurement. Included in the anlaysis of single-operator precision are first-crack strength, deflection, and toughness, the toughness index recommended by the American Concrete Institute Committee 544, and a number of other toughness indices that have been shown in a previous paper to define flexural toughness more completely. The single-operator 1S% value defined according to ASTM Standard Practice for Preparing Precision Statements for Test Methods for Construction Materials (C 670) is used as the measure of precision throughout, the bulk of the data being obtained from testing of 300- by 100- by 100-mm (12- by 4- by 4-in.) steel fiber reinforced beams under third-point loading. However, the effects of beam size, shape, span, and mode of loading on both the actual values of the toughness indices and their variability are also discussed. Single-operator levels of precision achievable in flexural toughness tests by an experienced operator using good equipment are summarized to provide input to precision statements for a future ASTM standard dealing with the measurement of flexural toughness under static loading.

Definition and Measurement of Flexural Toughness Parameters for Fiber Reinforced Concrete

Abstract Current and past approaches to assessing and defining the flexural toughness of fiber reinforced concrete are reviewed, and the difficulties associated with them are discussed. Refinements needed to ensure correct analysis and interpretation of load-deflection relationships in evaluation of flexural toughness are identified. A new system of defining toughness is proposed. It comprises a series of indices based on material behavior up to specified multiples of the first-crack deflection. This system is shown to be superior to the one currently advocated by The American Concrete Institute Committee 544 based on material behavior up to a deflection of 1.9 mm (0.075 in.). It is recommended as the basis for a standard test method to evaluate toughness, and appropriate provisions for inclusion in the standard are identified.