Aly Said

Resistance of Flat-Plate Buildings against Progressive Collapse. I: Modeling of Slab-Column Connections

AbstractA macromodel for slab-column connections is created for use in the system-level progressive collapse analyses of reinforced concrete flat-plate structures. The proposed model jointly uses shell and connector elements to simulate the complex behavior of slabs. Shell elements are used to simulate the flexural response of slab and the load redistribution over floor slabs. The connector elements, which permit simulating separation of slab from column on a punching failure, are defined with nonlinear responses for primary bending moment and torsion. A deformation-based punching failure criterion is defined for connector elements to simulate the punching failure at a slab-column connection and failure propagation. Parameters defining concrete tension stiffening behavior under static loading, including the peak tensile stress and the tensile strain when stress degrades to zero, are calibrated from two experiments. To ensure applicability, the proposed model is validated by 24 large-scale tests conducted ...

Effect of colloidal nano-silica on alkali–silica mitigation

Alkali–aggregate reaction was first observed in the US during 1920s. In the last decades, several studies investigated the mechanisms of alkali–silica reaction in concrete and the extent of damage it may cause to the cementitious matrix. Research on alkali–silica reaction mitigation covers mainly the use of supplementary cementitious materials and lithium compounds. However, with possible change in coal burning regulations and fly ash shortages in some areas, it is important to investigate approaches to mitigate ASR that involves lower amounts of supplementary cementitious materials. Furthermore, current research has shown the potential enhancements to concrete microstructure through the use of nano-silica. In the current study, the effect of using nano-silica on the alkali–silica reaction will be investigated. Preliminary results show that nano-silica can help mitigate the effect of alkali–silica reaction.

Factors Affecting the Selection of In-House and Outsourcing Road Maintenance Methods and Assessment of Their Benefits

AbstractIn the United States, for road maintenance activities, state departments of transportation (DOT) use either in-house resources or outsource to private contractors under various methods, such as method-based contracting (MBC), performance-based contracting (PBC), the hybrid method, lane rental, cost plus time, or incentives/disincentives, etc. In a literature review, factors were identified that affect the selection of the maintenance methods as well as their benefits. This study conducted a survey with state DOT maintenance engineers, and asked them to rate the factors and benefits. This study identified which factors were more important to state DOTs when assigning maintenance work to in-house staff or to private contractors. Statistical test results showed that the top two ranked factors influencing the selection of in-house (MBC and PBC) were availability of DOT staff and DOT staff have specific skills for jobs. Regarding the levels of satisfaction with benefits, on average, the respondents wer...

Innovative Polymer-Modified Pervious Concrete

The United States generates a tremendous amount of waste latex paint annually, which is a significant challenge to recycle as it contains volatile organic compounds. However, waste latex paint can be utilized to produce an economic latex-modified pervious concrete that is superior to regular pervious concrete. This study evaluates pervious concrete produced using waste latex paint in comparison to regular pervious concrete as well as that produced using commercially manufactured styrene-butadiene rubber. Waste latex paint added to concrete results in characteristics comparable to polymer-modified concrete made with commercial latex products.

Latex-Modified Concrete Overlays Using Recycled Waste Paint

Concrete overlays are exposed to aggressive environment and deicing salts combined with traffic loads. They are required to have high strength while exhibiting adequate durability. Furthermore, in the case of bridge deck overlays, they are required to have high abrasion resistance and low permeability to survive their service life and to avert salts leaching to the deck and the rest of the bridge superstructure. Poor performance of bridge overlays can result in bridge deck corrosion leading to replacement which is costly and can cause traffic interruption. Polymer-modified concrete is typically used in bridge deck overlays due to its superior tensile strength and low permeability. Polymer modification of concrete is performed by incorporating an appropriate dose of polymer during the mixing process, which adds to the cost of concrete. In this study, the use of waste latex paint to produce an economical polymer-modified concrete is performed. The resulting concrete is then compared to polymer-modified concrete produced using commercially available polymers in the market.

Physical salt attack on concrete incorporating nano-silica

The damage induced by crystallization of salts (physical salt attack, PSA) has been often misidentified as chemical attack. Under certain environmental conditions, PSA may cause notable surface damage of concrete partially embedded in salt-rich soils. The process is similar to salt weathering of natural rocks. The current study investigated the effect of refining the microstructure of concrete by nano-silica additions on its resistance to PSA in an accelerated procedure. Specimens were partially immersed in a high-concentration sodium sulphate solution and simultaneously exposed to cyclic temperature and relative humidity. Specimens’ deterioration was monitored for more than 100 cycles of exposure. Also, an effort was made to analyse the relationships between specimen damage, characteristics of pore structure and absorption capacity. Finally, the immersed and drying portions of specimens were tested by X-ray diffraction and Rietveld analysis and scanning electron microscopy to identify the root cause of damage.

Alkali-Silica Reaction Mitigation Using Nano-silica and Fly Ash

Alkali-aggregate reaction was first observed in the US during 1920s. In the last several decades, several studies investigated the mechanisms of alkali-silica reaction in concrete and the extent of damage it may cause to the cementitious matrix. Research on alkali-silica reaction mitigation covers mainly the use of supplementary cementitious materials and lithium compounds. Meanwhile, nano-silica has proved its capacity to enhance concrete properties. Nano-silica consists of highly reactive high surface area particles generally available dispersed in a solution. The addition of nano-silica to concrete can significantly enhance the overall cementitious matrix and the interfacial transition zone in specific. Such enhancements can lead to refined pore structure, lower overall permeability and higher strength. The use of nano-silica in infrastructure project promises longer service life with low maintenance activities resulting in substantial economic savings. In the current study, the use of effect of nano-silica on the alkali-silica reaction will be investigated. Results show that nano-silica can help mitigate the effect of alkali-silica reaction.