International Concrete Abstracts Portal

This CD-ROM contains nine papers sponsored by ACI Committee 548. The extended use of polymers in concrete has grown significantly in the last two decades. This is demonstrated from the common use of epoxy to repair cracks, to the use of polymer concrete overlays to protect bridge decks. The papers provide insight into the current state of research and development for the use of polymers in concrete and new trends that will shape the frontiers of the polymer concrete industry in the near future. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-278

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.

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.

Concrete mixtures, having a water/cement ratio below 0.4, may exhibit a considerable autogenous shrinkage induced by internal drying of the capillary pore structure. In order to compete with this issue and to avoid or compensate for the development of autogenous shrinkage of concrete, either the mix proportions have to be adapted or additional (internal) water has to be supplied with emphasis on the moisture state of the capillary pore system. Until recently, one of the most frequently used methods used to retain internal self-desiccation of concretes was by adding water saturated porous light weight coarse aggregates (i.e. Lytag) or wood pulp fibers to the cementitious matrix. One of the latest innovations in this area is the addition of shrinkage reducing additives such as Super Absorbent Polymers (SAP). In order to examine the pros and cons of SAP addition to a concrete mix, an extensive experimental programme considering eight different concrete mixtures have been tested at Delft University of Technology. It is investigated how the Super Absorbent Polymers influence the mechanical and viscoelastic properties of hardening concrete. Experiments are performed for water/cement ratios of 0.32, 0.39 and 0.5, for Portland cement as well as Blast Furnace Slag cement, with addition of three different percentages of SAP, i.e. 1, 1.5 and 2 kg/m3 (1.68, 2.53 and 3.37 lb/yd3). The mixtures are tested at isothermal conditions of 20 ºC and the early-age autogenous shrinkage strains are measured over a testing period of about 300 hours. Besides, the tensile strength, compressive strength, the elastic modulus and the creep strains have been measured for the different mixtures as well. The tensile, compressive strength and elastic modulus are tested at 28 days of age. The early age creep of the mixtures was measured from prisms and tested under a sustained compressive load of 40% of the compressive strength and were loaded at an age of 3 and 7 days. In this paper, the results of the experimental program are described in detail. A significant effect of the reduction of autogenous shrinkage due to SAP addition was observed. However, results also show that SAP affects the tensile and compressive strength and the viscoelastic properties like elastic modulus and the early age creep.

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.