International Concrete Abstracts Portal

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.

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.

Hydraulic cement concrete overlays made with latex-modified concrete (LMC) and silica fume concrete (SFC) are typically used to extend the life of bridge decks because the overlays reduce the infiltration of water and chloride ions. Rapid concrete overlays can be used to reduce lane closure time and associated traffic congestion and road user costs. LMC prepared with very early hardening cement (LMC-VE) has been used as a rapid overlay for bridge decks in Virginia since 1997. This paper compares the performance of LMC-VE overlays to that of conventional LMC and SFC overlays. Results indicate that LMC-VE overlays are performing as well or better than LMC and SFC overlays. LMC-VE has become a standard overlay for situations in which lane closures cause major traffic congestion. The higher cost of materials for LMC-VE overlays can be off set by lower costs for traffic control. Including user cost savings make LMC-VE overlays even more cost effective.

It is generally accepted that the latex-modified concrete (LMC) overlay is a superior protection system for bridge decks. The incorporated latex acts as a plasticizing agent providing good workability even for low water/cement ratios. When exposed to air, the latex polymerizes forming a membrane around the hydration products resulting in a lower permeability and inherent flexibility to resist freeze and thaw cycles. Nevertheless, the latex imposes constructability limitations that dramatically increase the initial installation cost of the LMC overlay. The latex starts to polymerize within 15-30 minutes dictating the need for mobile mixers to install the LMC overlay. The cost of the latex adds to the cost of the LMC especially when the oil price increases. This paper presents and discusses the effect of different types and combinations of macro and micro synthetic fibers on the major performance characteristics and constructability of the fibrous LMC overlay.

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.