Analysis and Evaluation of the Development of Various k-Values for Use in Design

Inconsistency exists between common conversions from soil index properties (e.g., CBR) to a design k-value and a widespread nomograph that has become the definitive industry reference on the topic in the United States. Propagation of these inconsistencies into guidance from groups like the American Concrete Pavement Association (ACPA) and American Concrete Institute (ACI) Committees 330 and 360 has contributed to confusion in the industry. Advancements between the pavement and slab-on-ground communities have occurred in parallel but are inconsistent with each other, thus adding more confusion. ACPA developed a conversion set to better align the industry on a static k-value for design. While the ACPA model is included in StreetPave, PavementDesigner.org, and the ACPA App Library, outdated conversion equations are frequently used due to familiarity and lack of understanding of the underlying principles. This paper presents a summary of the industry's prior practices and recommendations, a detailing of the approach proposed by ACPA, and guidance on which k-value is recommended for design of concrete pavements and slabs-on-ground.

Evaluación de concreto elaborado con agregados de canteras de río y de cerro de los Andes del norte de Perú

El concreto es un material versátil, y debido a que se encuentra en todo tipo de construcción su demanda ha aumentado, generando así un incremento en la extracción de agregados, los cuales muchas veces no cumplen con las especificaciones técnicas. Se tuvo por objetivo evaluar comparativamente concretos elaborados con canteras de cerro y de río, para diseños con resistencia a la compresión (f’c) = 175 kg/cm2 y f’c = 210 kg/cm2. Se analizó las propiedades de los agregados tanto de cerro como de río, para calcular la dosificación de los componentes, utilizando la metodología del comité 211 del American Concrete Institute (ACI); luego de la elaboración de las probetas se realizó el curado y posteriormente se realizó los ensayos de resistencia a la compresión a los 7, 14 y 28 días. Se determinó que el concreto elaborado con agregados de río cumplen con los parámetros mínimos de resistencia a la compresión; sin embargo, los agregados en su mayoría no cumplen con la Norma Técnica Peruana (NTP) 400.037 y esto repercute de forma negativa en la resistencia del concreto. Por lo tanto, se recomienda la utilización de los agregados de cerro teniendo en cuenta las respectivas correcciones en el diseño de mezcla para obtener concretos con resistencias requeridas.

Penggunaan Geotextile Sebagai Perkuatan Pada Silinder Beton Mutu Normal

Karena adanya transformasi beban suatu susunan pada infrastruktur bangunan dapat menerima beban diluar rencana awal, untuk itu perlu dilakukan perkuatan struktur agar struktur bangunan tetap aman. Dalam penelitian ini penggunaan serat woven & non woven pada beton baru diharapkan bisa menambah kuat tekan, kuat tarik belah dan modulus elastisitas terhadap beton konvensional. Mix design penelitian ini menggunakan metode American Concrete Institute (ACI). Sampel uji berjumlah 36 kemudian dibagi menjadi 3 variasi. Hasil penelitian ini telah menunjukkan penambahan kuat tekan, kuat tarik belah, dan modulus elastisitas. Kuat tekan untuk woven meningkat 29,485% % dan non woven meningkat 7,296% %, kuat tarik belah untuk woven meningkat 24,633% dan non woven meningkat 5,285%., modulus elastisitas untuk woven meningkat 20,924% dan non woven meningkat 9,356% . Untuk perbandingan kedua material, woven lebih kuat daripada non woven.

Comparison between the British and American Methods in Designing Concrete using Local Aggregate in the City of Mosul Preparation

This research included an applied study for the design of concrete mixtures by following the method of the American Concrete Institute (ACl) and the method of the Building Research Center in England (British method) to restriction which of these two methods is more suitable for use and application in the design of concrete mixtures when using local aggregate (gravel and sand taken from the area Badush and Aski Mosul), where job mixes were made using the mixing ratios obtained from these two methods, and a comparative study was made for the properties concrete resulting in the soft state (workability )and the hardened state (compressive resistance), and the results proved the following: A- In general, when discussing the results according to mixing ratios and workability levels, the method of the Building Research Center in England (the British method) gave higher results than the results obtained by the American Concrete Institute method (the American method) when using the above local aggregate whereas results shown increase in (workability) and Compressive strength. This increase amounts to the percentages shown in the table below: Compressive strength (%) Slump test (%) workability 10.48 14.40 Precipitation = 10-8 cm 12.10 21.40 Precipitation = 18-15 cm Table (1-1) B- It is possible to make another comparison, when fixing the proportion of water/cement, it turns out that the method of the Building Research Center in England (the British method) gives higher workability than the method of the American Concrete Institute (the American method) and for the same proportion of cement/ water, the American method gives Higher compressive strength than the British method. C- The building research center method is a more practical and applicable method more than the American Concrete Institute method because it takes the type of cement, the type of aggregate and other properties of the aggregate (especially particle shape) into consideration

Local Behavior of Lap-Spliced Deformed Rebars in Reinforced Concrete Beams

Twelve full-scale reinforced concrete beams with two tension lap splices were constructed and tested under a four-point loading test. Half of these beams had shorter lap splices than that recommended by American Concrete Institute Building Code ACI 318-19; they failed by bond loss between steel and concrete at the lap splice region before rebar yielding. The other half of the beams were designed with a lap splice length slightly exceeding that recommended by ACI 318-19; they failed by rebar yielding and exhibited a ductile behavior. Several strain gauges were attached to the longitudinal bars in the lap splice region to study the local behavior of deformed bars during loading. The strain in a rebar was maximum at the loaded end of the lap splice and progressively decreased toward the unloaded end because the rebar at this end could not sustain any load. Stress flow discontinuity occurred at the loaded end and caused stress concentration. The effect of this concentration was investigated based on test results. The comparison of bond strengths calculated by existing equations and those of tested specimens indicated that the results agreed well.

Air Content in Fresh Air-Entraining Cement Mortars

The durability of a cement composite is the most important criterion for assessing this material. However, due to the durability of the cement composite, its frost resistance is an important property. In order to ensure concrete frost resistance, the European standard PN-EN 206-1: 2013 requires its aeration at the level of 4 - 7%. The Committee 201 of the American Concrete Institute (ACI) also requires the use of an air-entraining admixture in concretes exposed to frost damage. The amount of air-entraining admixture is significantly influenced by the composition of the cement used. In order to minimize the problems with obtaining frostresistant concrete, an attempt was made to create air-entraining cements. This article presents the effect of the amount and type of dosing of air-entraining admixtures (natural and synthetic) on the air content in fresh air-entraining cement mortars. The test cements used also differed in the production method: joint mixing of components and joint grinding of components. Based on the research, a lot of valuable information was obtained related to the influence of the preparation of air-entraining cements on the air content in the mortar, e.g. mortars with mixed cement with natural air-entraining admixture have a higher air content. The air content is higher in the cement co-ground with natural air-entraining admixture. A synthetic air entraining admixture added separately to mixed cements with silica fly ash and ground granulated blast furnace slag increases air entrainment in mortars. The synthetic air-entraining admixture added separately to co-milled cements causes an increase in air entrainment in the mortars, except for those containing cement with ground granular blast furnace slag.

Modified Falling Mass Impact Test Performance on Functionally Graded Two Stage Aggregate Fibrous Concrete

This research examined the performance of functionally graded two-stage fibrous concrete (FTSFC) against modified repeated falling-mass impacts. This study led to the concept of creating improved multiphysics model of fibre composites with better impact resistance for potential protective constructions. FTSFC was developed based on the bio-inspiring strength of turtle shells. The excellent impact resistance of FTSFC was accomplished by including a larger quantity of steel and polypropylene fibres in the outer layers. At the same time, one- and two-layered concrete were cast and compared to evaluate the efficiency of three-layered FTSFC. To minimize the dispersed test results, a modified form of the 544 drop-mass impact test was recommended by the American Concrete Institute (ACI). The modification was a knife-edge notched specimen instead of a solid cylindrical specimen without a notch. This modification predefined a crack path and reduced the dispersion of results. Cracking and failure impact numbers, ductility index, and failure mode were the testing criteria. The suggested modification to the ACI impact test decreased the coefficient of variance, showing that the dispersion of test results was reduced significantly. This study led to the concept of creating improved, fibre composites with better impact resistance for potential protective constructions.

An Experimental Investigation on Concrete Filled Steel Tube Columns Under Axial Compression

This paper presents an experimental investigation on the behaviour of concrete filled steel tube columns under axial compression. The steel columns were filled with self-compacting and self-curing concrete instead of normal conventional concrete. A test program consisting of square column, circular column and rectangular column was firstly conducted. The behaviour of three concrete filled steel tubular sections (CFSTs) under axial load is presented. The effect of steel tube dimensions, shapes and confinement of concrete are also examined. Measured column strengths are compared with the values predicted by Euro code 4 and American codes. Euro code 4, gives good estimation of self-compaction concrete. However, lower values as measured during the experiments were predicted by the American Concrete Institute (ACI) equation. Also, the effect of thickness of steel tubes, concrete cube strength and steel percentage is also studied. In addition to CFST column the steel tube also acts as confinement for concrete.

Multivariable Regression Strength Model for Steel Fiber-Reinforced Concrete Beams under Torsion

Torsional behavior and an analysis of steel fiber reinforced concrete (SFRC) beams are investigated in this paper. The purpose of this study is twofold: to examine the torsion strength models for SFRC beams available in the literature and to address properly verified design formulations for SFRC beams under torsion. A total of 210 SFRC beams tested under torsion from 16 different experimental investigations around the world are compiled. The few strength models available from the literature are adapted herein and are used to calculate the torsional strength of the beams. The predicted strength is compared with the experimental values measured by the performed torsional tests and these comparisons showed room for improvement. First, a proposed model is based on optimizing the constants of the existing formulations using multi-linear regression. Furthermore, a second model is proposed, which is based on modifying the American Concrete Institute (ACI) design code for reinforced concrete (RC) members to include the effect of steel fibers on the torsional capacity of SFRC beams. Applications of the proposed models showed better compliance and consistency with the experimental results compared to the available design models, providing safe and verified predictions. Furthermore, the second model implements the ACI code for RC using a simple and easy-to-apply formulation.

Buckling of Spherical Concrete Shells

This study is focused on the buckling behavior of spherical concrete shells (domes) under different loading conditions. The background of analytical analysis and recommended equations for calculation of design buckling pressure for spherical shells are discussed in this study. The finite element (FE) method is used to study the linear and nonlinear response of spherical concrete shells under different vertical and horizontal load combination buckling analysis. The effect of different domes support conditions are considered and investigated in this study. Several dome configurations with different geometry specifications are used in this study to attain reliable results. The resulted buckling pressures from linear FE analysis for all the cases are close to the analytical equations for elastic behavior of spherical shells. The results of this study show that geometric nonlinearity widely affects the buckling resistance of the spherical shells. The effect of horizontal loads due to horizontal component of earthquake is not currently considered in the recommended equation by The American Concrete Institute (ACI) to design spherical concrete shells against buckling. However, the results of this study show that horizontal loads have a major effect on buckling pressure and it could not be ignored.