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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Showing 1-5 of 10 Abstracts search results
March 1, 2011
A.S. El-Dieb, T.A. El-Maaddawy and A.A.M. Mahmoud
Maintaining satisfactory moisture content in concrete during its early ages is very important to develop required properties. Retaining free water of the mixture for a longer period will have a beneficial effect similar to that of curing. Self-curing mixtures will be very beneficial especially in regions where water is not adequately available. Polymers in concrete have received considerable attention over the past two decades. This study investigates using laboratory synthesized water-soluble polymers: polyethylene glycol (PEG) and polyacrylamide (PAM) as self-curing agents and its effect on the degree of hydration, water absorption, permeable pores and microstructural characteristics of Portland cement mixtures without and with 8% silica fume replacement. Portland cement mixtures including PEG or PEG+PAM as self-curing agents showed a better quality compared to that of the non-cured mixtures. Mixtures incorporating 8% silica fume including a mixture of PEG and PAM as self-curing agent had a better quality compared to that of the mixture including only PEG especially at later ages.
E.M. Soliman, U.F. Kandil and M.M. Reda Taha
This research examines the significance of using carbon nanotubes (CNTs) on the mechanical characteristics and microstructural features of latex modified mortar (LMM). CNTs have been introduced recently as a new nanoscale material with excellent mechanical properties. This work examines the ability of various CNTs’ contents to alter the mechanical properties of latex modified mortars. Compression and tension tests were performed on LMM specimens with and without CNTs at 7 and 28 days of age. The experimental investigations showed that CNTs can enhance the strength and deformation characteristics of LMM. Microstructural investigations showed CNTs to be well dispersed and bonded to the polymer latex matrix. It is concluded that CNTs can be a useful alternative to enhance the mechanical characteristics of polymer modified cement composites.
D.W. Fowler and D.P. Whitney
Thin polymer concrete overlays (TPCOs) consist of a polymer binder and aggregates with a thickness of 1 inch (25 mm) or less. They have been widely used for providing long-lasting wearing surfaces for bridge decks. Their advantages include adding little dead load; very fast cure; shallow depths that eliminate raising approach slabs and permitting the transition from overlaid lane to non-overlaid lane during construction; excellent bond to concrete; very low permeability; and excellent skid resistance. Over 2200 have been installed in the U.S. and Canada, and they have become a recognized method for extending the lives of bridges. The state of practice has become well established. Evaluation of the substrate, repair of the substrate, and surface preparation are essential to having a sound surface for applying the TPCOs. The three types of overlays normally used are multiple layer, slurry and premixed. Epoxies are the most widely used resins although methacrylates and polyester styrenes are used for some applications. Resin application rates and aggregate gradings and application rates are also quite important.
Moisture transport, shrinkage and creep in repair material have a profound influence on long-term durability and serviceability of patch repair in concrete structures. In the process of drying of a newly cast repair mortar, the moisture diffuses within the domain and convects at the bounding surfaces resulting in hygral gradient across the depth and coupled drying shrinkage. This leads to the generation of tensile stresses in the repair layer, and cracks are developed at the surface of patch repair and at its interface with the parent concrete. Polymer-based repair materials also undergo significant shrinkage and tensile creep, which influences the stresses and cracking in the repair overlays. Experimental investigations including strength tests, moisture loss, shrinkage, and creep measurements were conducted on four selected repair mortar including two polymer-based repair mortars. These tests provide the parameters required for computation of stresses and prediction of cracking in repair overlays. Nonlinear finite element based diffusion analysis and experimentally obtained drying curves can be used to develop the empirical moisture diffusivity law and quantification of the surface transfer coefficient which is used for prediction of moisture loss in a repair layer. Multiphysics finite element software COMSOL provides a convenient tool for computation of moisture transport and associated evolution of stresses due to shrinkage in a composite system in which a polymer based repair mortar is used for patch repair of a concrete member.
J. Belkowitz, M. Best, M. Nilsen, F. Fisher and D. Armentrout
The following paper documents the preliminary experimentation and analysis of a polymer fortified hydrated cement sample. Concrete is a brittle construction material. When compared to other construction materials, concrete can offer competitive structural resistance under compressive loads. But due to the brittle nature of the hydrated cement matrix, C-S-H network, concrete is poor when resisting flexural loads. The brittle C-S-H structures cannot absorb the flexural energy like a ductile material. The properties of concrete fracture are analyzed at the microscopic level to understand the method of failure. By including the acrylic polymer into the hydrated specimens it was the belief of the authors that the acrylic polymer would enhance the fracture behaviour of the concrete in flexure. The C-S-H hydrates precipitate from a saturated solution. The acrylic polymer, after being mixed into the cement paste while still fresh, becomes secured in the C-S-H structure as said structure hardens. Samples were cast, cured, and tested in order to determine if the acrylic polymer cause the C-S-H structure to behave in a ductile manner. The testing included compressive and flexural stress tests with microstructure observation via Scanning Electron Microscope (SEM). The compressive and flexural tests were used to discern a measured value of gain when using an acrylic polymer compared to a control mix. The SEM images were used to determine crack origin, type of failure, and acrylic polymer benefit. The tests and SEM images revealed that there was a negative reaction between the admixtures to cause an excessive air generation. Despite the setback, the SEM images revealed evidence of energy absorbing of the acrylic polymer mix.
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