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International Concrete Abstracts Portal

Showing 1-5 of 105 Abstracts search results

Document: 

SP-344_10

Date: 

October 1, 2020

Author(s):

Gary G. Greene, Jr. and David L. Hartmann

Publication:

Symposium Papers

Volume:

344

Abstract:

The Joint ACI-ASCE Committee 445 published a document titled Report on Torsion in Structural Concrete that contained an in-depth review of historical theory development, design models, and simplified design procedures for the effect of torsion in concrete structures. That document contained three design examples that were relatively simple. An important goal of this ACI Special Publication is to provide more realistic design examples that are usable by design professionals. This paper satisfies that goal by showing a detailed solution to a realistic example that has been encountered on several occasions by one of the authors. Another goal of the ACI Special Publication is to show applications where torsion is combined with flexure and shear. In this example, the torsional effects are combined with biaxial flexure and biaxial shear forces. This example includes a check of the new provisions in ACI 318-19 for bi-axial shear effects.

This paper shows a detailed solution for the design of a reinforced concrete grade beam subjected to torsional effects combined with biaxial shear and biaxial flexure. The grade beam is a portion of a structural screen wall system. A 25 psf (1.20 kPa) strength level wind pressure acts on a 20 ft (6.10 m) tall CMU wall supported by a continuous grade beam. The 21 in (533 mm) wide by 18 in (457 mm) deep grade beam is isolated from an expansive soil and is supported by drilled shafts 21 ft (6.40 m) on center. The wind load and gravity loads induce torsion, biaxial bending moments, and biaxial shear forces in the grade beam. This example shows how to calculate the internal forces in the grade beam at the critical section and design the required longitudinal and shear reinforcement according to the ACI 318-19 code.

The design of the grade beam includes closed stirrups of #4 (Ø 12) bars spaced at 5.5 in (140 mm), five #8 (Ø 25) bars used near the top and bottom faces and one #6 (Ø 16) bar used at mid-height near the side faces.


Document: 

SP331-04

Date: 

February 1, 2019

Author(s):

Mark E. Williams

Publication:

Symposium Papers

Volume:

331

Abstract:

Bridge embankments serve a vital role in raising the roadway profile to the bridge deck elevation for passage of vehicles. It is common practice to construct embankments utilizing compacted lifts of soil obtained from nearby borrow pits. Soil borrowed from regions of predominantly expansive clay soils can be problematic for bridge embankment construction. High plasticity soils swell in contact with moisture, inducing vertical and lateral pressure on embankments. Mechanically Stabilized Earth (MSE) walls are particularly susceptible to soil expansion as they try to confine high soil expansion pressures through soil reinforcement and mobilization of a stabilized volume behind the face of the wall. This paper provides insight into the investigation of MSE wall movement, abutment movement and corresponding bridge beam distress, and reinforced concrete failures resulting from high plasticity soil backfill in existing bridge embankments. Remediation strategies are discussed which are directed at the expansive soil behavior within the embankment.


Document: 

SP326-09

Date: 

August 10, 2018

Author(s):

Stephen O. Ekolu

Publication:

Symposium Papers

Volume:

326

Abstract:

Investigations were conducted to evaluate the effects of synthetic zeolite additive on delayed ettrintite formation (DEF) in heat cured cementitiuous systems. Mortar prisms 25 x 25 x 285 mm (1 x 1 x 11.4 in.) were prepared at water-cement ratio (w/c) = 0.5, using portland cement CEM I 42.5 N,R. Sulphates were introduced into the mixtures by adding 2%, 3% and 5%SO3. Also, a commercially available synthetic zeolite additive PWC was added to cement at proportions of 1%, 0.5% and 2.5%PWC. The mortar specimen were heat-treated at 95oC (203oF) then stored in water.

It was found that heat treatment led to higher early strength gain as expected but increase in sulphate concentration correspondingly caused reduction in early strength development. There was a marked increase in early strength of heat-cured mortars containing PWC. Use of 2.5% PWC in expansive mortars led to five-fold increase in expansion at 90 days. Accordingly, preliminary results indicate a possibility of adverse effect of PWC on DEF in cementitious systems, especially when used in elevated proportions. Further investigations are needed to conduct detailed evaluation of PWC effect on DEF.


Document: 

SP-320_45

Date: 

August 1, 2017

Author(s):

Isabelle Fily-Paré, Benoît Fournier, Josée Duchesne, Arezki Tagnit-Hamou

Publication:

Symposium Papers

Volume:

320

Abstract:

Finely ground glass produced from recycling facilities is an alternative supplementary cementing material that is often considered for eco-friendly concrete mix designs. However, documentation on its behaviour in concrete is limited or somewhat contradictory. Many studies suggest that glass powder can suppress the expansion of concrete due to alkali-silica reaction (ASR), while others suggest that its high alkali content maintains the expansive potential in concrete due to ASR and consequently limits its preventive character. The present work seeks to clarify the overall availability of alkalis in the pore solution of cementitious matrices incorporating glass powder. For this purpose, pore solution extraction had been conducted, on pastes containing 0%, 20% and 40% of Glass Powder and cements of alkali levels of 0.25%, 0.63%, 0.94% and 1.25% Na2Oe. The concentration of alkalis available in the pore solution was analysed after 28 and 91 days. Results showed that the effect of GP on the hydroxyl concentration of the pore solution is limited for cement of high alkali content and important for low alkali cement. Also GP tends to reduce the potassium concentration and increase the sodium concentration of the pore solution.


Document: 

SP317-02

Date: 

June 1, 2017

Author(s):

R. Brett Holland, Kimberly E. Kurtis, and Lawrence F. Kahn

Publication:

Symposium Papers

Volume:

317

Abstract:

Due to the increasing costs of maintaining deteriorating infrastructure, there has been an increased importance placed on the durability of new concrete structures. For marine structures and structures constructed in sulfate rich soils, sulfate attack can cause the structure to degrade over time. Historically, sulfate attack resistance has been evaluated using an expansion test method. However, in addition to expansion during sulfate attack, concrete can exhibit strength degradation without expansion. Resistance to sulfate attack was assessed using both expansion and strength degradation test methods for thirteen binder compositions. Results were compared to established criteria for expansion and proposed criteria for change in strength and were correlated to overall binder composition, considering the combination of three cement types and five supplementary cementitious materials (SCMs). Compressive strength degradation testing demonstrated that mix designs with a high initial CaO content, determined through oxide analysis of the cement and SCMs, performed well, presumably due to the formation of calcium hydroxide (CH) which served as a buffer to the decalcification of calcium-silicate-hydrate (C-S-H) in the formation of gypsum. However, high CaO contents led to poor performance on expansion testing due to the availability of large amounts of calcium hydroxide to react with sulfate ions to form expansive ettringite. Slag mix designs containing metakaolin performed well on both criteria.


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