International Concrete Abstracts Portal

The shortage of high-quality fine aggregate as an essential component of concrete has become an emerging worldwide concern for the construction industry. Concrete typically comprises up to 30% fine aggregate, which largely influences the strength and durability of the final product. Therefore, finding suitable substitutes for natural fine aggregate has become an important aspect of current concrete research.

In this study, we investigated the suitability of using remediated thermal-treated soil and tar-containing asphalt as secondary raw materials in a self-compacting concrete (SCC) mixture. The remediated materials were used as both (1) fine aggregate replacement to replace all the river sand and (2) partial filler/supplementary cementitious material (SCM) replacement. The modified Andreasen and Andersen (A&A) particle packing model was used to determine the optimal replacement level. Based on the optimal mixture design, the impact of the replacement on the fresh and mechanical properties of SCC was evaluated. Additionally, the pozzolanic reactivity of the fine fraction (<125 μm) within the secondary sand was assessed and compared to that of limestone powder. Our findings confirm that using remediated thermal-treated soil and tar-containing asphalt can produce a more circular, sustainable SCC by replacing high-quality natural sand and limestone filler and reducing the environmental impact of conventional SCC. This study contributes to finding viable alternatives to natural fine aggregate and promotes the use of recycled materials in construction.

The uncontrolled urban development of the last century caused high land consumption and strong non-renewable natural raw materials utilization. To solve the problems generated by soil sealing, the building sector has developed a pervious concrete manufactured with Portland cement and natural aggregates. Although this mixture mitigates the effects of soil sealing, the production of a Portland-based pervious concrete has a strong environmental impact.

The purpose of this research is to investigate an alkali-activated slag-based pervious concrete (AASPC) manufactured with tunnel muck (TM) as recycled aggregate instead of natural sand and gravel and to evaluate the relationship between aggregate size and physico-mechanical properties of no-fines concrete.

Six different single-sized recycled aggregates from tunneling works (drilling and blasting technique) were used to produce six different AASPCs that were characterized in terms of compressive strength, porosity, and water permeability under constant and variable flow.

Experimental results evidenced that the average size of aggregates strongly influences the open and total porosity of the materials, thus determining very different compressive strengths (from about 6 MPa for concrete with 16-22 mm gravel to 20 MPa for concrete made with 1-2 mm sand) and water permeability. Finally, the environmental impact of these mixtures (energy requirements, CO₂ emissions, and natural raw materials consumption) is strongly reduced in comparison to traditional Portland-based no-fines concrete at equal strength class.

Pavement subgrade is an in-situ material upon which the pavement structure is constructed. A soil with a high plasticity index will experience high shrinkage and swell depending upon its moisture content with detrimental impacts on its supported pavement structure. Removing and replacing the weak soil with better-quality soil is an alternative to stabilization of poor subgrade soil and may be a very expensive solution, typically for large road networks. Secondly, stabilization of weak soil -subgrade using conventional cement may not be sustainable due to its high CO₂ footprint. The feasibility of this non-conventional method using blended geopolymer binder for stabilization of weak subgrade soil was investigated compared to the conventional cement stabilization method. Laboratory testing of design mixes included unconfined compression test, maximum dry density, CBR and shrink & swell testing determining its feasibility and optimum extent. This research paper will present the findings on the effectiveness of blended geopolymer (fly ash and slag) as an alternative to conventional cement-based soil stabilizers for weak subgrade and its sustainability potential.

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.

The use of a Performance-Based Seismic Design (PBSD) approach to design buildings that exceed 240-feet (73.2 m) tall has been common among many west coast cities. More recently, Oakland, California has been an epicenter of development that has created a market for taller buildings. The residential tower at 1640 Broadway, which is currently under construction, is the first tower designed using PBSD exceeding 240-feet (73.2 m) tall in Oakland. This is notable in terms of establishing the implementation of PBSD in a new jurisdiction. This is also notable because of the near fault location of Oakland, given that the Hayward fault is less than 3.1 miles (5 km) from the downtown region, which raises new issues such as fault normal/fault parallel ground motion scaling issues and designing for extremely high demand levels. Due to these extreme demand levels, the project consisted of high reinforcement ratios within the walls and embedded steel coupling beams. Finally, the foundation conditions were challenged by the proximity to BART tunnels and therefore consist of a hybrid mat foundation supported on deep soil mixed panels and cased steel piles. A summary of the unique aspects of the building are presented and compared with typical code compliant and PBSD towers.