Why "polymer concrete"? Well, because I have spent most of my working career specializing in structural uses for polymer concrete (PC). Polymer concrete is one of the newest construction materials. It was first used commercially in the United States in the 1950's. "Ar-Lite Panelcraft" polymer concrete building panels were manufactured then by Architectural Research Corporation and were marketed worldwide by the 1970's. Other early uses included highway patching, bridge deck repairs and bridge overlays. PC is now also used to precast underground structures, drains, highway products, corrosion resistant tanks, machine tool bases, cultured marble products, etc.
Polymer concrete is mixed and cast into formwork much like conventional portland cement concrete. It is a composite material consisting of graded aggregates, fillers and a polymeric binder. PC gains its usefulness from its relatively high strength, its durability, and its fast curing time. Its strength properties are quite similar to those of wood. PC is much more difficult to formulate and cast than conventional concrete since its hardening depends upon a complex organic chemical reaction that is influenced by the mix constituents, the make-up of the polymer being used and by environmental factors. Some of the ingredients are toxic and some are flammable before the hardening process (ie, don't try this at home!). Once hardened, however, PC becomes very safe and inert, leading to its good performance in many aggressive environments.
Since PC can be cast into any shape, it is a very valuable construction material. By analysis, section requirements can be determined and cast to shape without surplus material. Since PC is stronger by a factor of 3 to 5 times than portland cement concrete, the resulting structures are much lighter. This is beneficial where installation equipment and time are costly.
These characteristics make PC an ideal material for underground structures. CDR Systems Corporation, a leading US precaster, specializes in underground products made from hybrids of PC and other high performance composites. They have over 20 years of experience in design and fabrication of standard and custom underground structures. CDR has manufacturing plants on the east and west coasts and in the mid west to serve the entire US. Look at
CDR Systems Corporation for more information.
In 1978, I wrote an article for "Concrete Construction" magazine, part of which follows:
The dictionary defines "concrete" as a material formed by coalescence of separate particles in to a solid mass. Common usage of the word "concrete" in the construction industry refers to the formation of an artificial stone-like material by binding together aggregate particles with a cementitious matrix. This matrix has normally been formed through the hydration of portland cement. Formation of concretes with compressive strength of 15,000 psi and higher are now possible by replacing or assisting portland cement in providing the cementing matrix. Replace portland cement with polymers and you have polymer concrete. Impregnate portland cement concrete with polymers and you have polymer impregnated concrete. Replace the cement and water nozzle on shotcreting equipment with a polymer nozzle and you have polymer shotcrete.
Although it sounds simple enough, use of polymers in concrete involves a mixture of applied chemistry and normal concrete construction procedures. Basically defined, a polymer is a hardened or polymerized plastic; the product of a large number of monomeric molecules atomically chained together. So then, in order to use polymers in concrete, they must be used as monomers which are the simplest basic molecules of a material that can be combined to form large molecules of a stable material. These monomers must be chemically manipulated in the field to cause them to convert to the high molecular weight polymer required to produce concrete.
The first sample of polymer impregnated concrete was produced at Brookhaven National Laboratory in 1965 and the first measurements of the physical and durability properties were conducted in 1966 by the Bureau of Reclamation. The Federal Highway Administration, The U.S. Atomic Energy Commission, The Bureau of Reclamation, The Office of Saline Water, and The U.S. Army Corps of Engineers, through joint efforts, have been developing and evaluating materials and process information for a number of applications since 1965. To date, the technology of polymers in concrete have been used to substantially reduce water erosion to large hydraulic structures, to protect highway bridge decks from salt induced corrosion of the reinforcing steel, to produce high strength, water-tight tunnel liners, to restore severally deteriorated concrete buildings and as industrial floor overlays where normal concrete is subject to a hostile environment. This discussion will address the last two applications in particular, that of restoring buildings and in producing high strength, fast setting industrial floor overlays.
Polymer impregnated concrete (PIC) can be used to restore strength to a deteriorated concrete structure. Using PIC techniques concrete compressive strength can be increased dramatically by full depth treatment of the existing in place concrete. This procedure offers the advantage of not having to remove or demolish structures or structural elements when they are badly deteriorated. Therefore the use of the structure can continue, practically uninterupted, while restoration takes place and the resulting finished product has a higher strength than that of the initial structure.
Polymer impregnation is performed by a process involving several steps. First the concrete is thoroughly dried so that its in place moisture content is less than 3% by weight. (Preferably the moisture content should be reduced to approximately 1% by weight for best results.) Next the concrete is impregnated with a monomer system which consists of a basic monomer with several monomeric additives, to produce the final properties required, and a catalyzing agent. On horizontal surfaces, the monomer is installed simply by flooding the surface and allowing sufficient time for the monomer to soak into the concrete. Full depth penetration of a six inch high strength portland cement concrete slab has been achieved in approximately 4 days and lesser depths have been achieved in as little as six hours impregnation time. Once the monomer has soaked into the desired depth and loading, it is polymerized by the addition of heat. Normally the systems used required heating to approximately 160 degrees F.. This can be accomplished by any heating technique that isolates the high temperature areas of the heater from the concrete being heated.
A full scale test of PIC techniques demonstrate that they are applicable and can be successfully used for repair of extremely porous, low-strength concrete. The first such project using polymer impregnation in a building was the impregnation of a structural slab in the Cass County Jail Building in Fargo, North Dakota. This building had been condemned due to the severally deteriorated condition of the concrete and was subject to demolition. By incorporating PIC into the repair procedures, the structure was salvageable and the complete structural restoration cost was approximately $220,000 compared with the alternative of demolishing and replacing the structure of an estimated cost of $4,000,000.
Concrete buildings with structural deficiencies that have been deemed irreparable heretofore and that are otherwise suitable for restoration and continued use may now be evaluated for structural repairs using PIC techniques. When evaluating such concrete building for this type of restoration, however, the following characteristics should be carefully considered:
1. The economic feasibility of repairs,
2. The porosity and moisture content of the concrete to be impregnated,
3. Strength gains required to restore the structure, and
4. The safety of the process and techniques to be used.
Polymers may also be incorporated into the production of a concrete mix by replacing portland cement. This material is called polymer concrete. Depending on the monomer formulation and aggregate system used, polymer concrete can achieve strengths of 9000 to 15,000 psi in as little as 5 minutes or as long as several hours. Since the monomer is lower in viscosity than water, some saturation of the existing surface is achieved and this results in a superior bond between the polymer concrete and the conventional concrete substrata. Used as an overlay in structures, dams, or bridges, polymer concrete produces an extremely high strength durable wearing surface that is waterproof and therefore impervious to salt water penetration. Polymer concrete is prepared by either mixing the monomer directly with the aggregate system in a mixer and placing it in a manner similar to conventional concrete or by preplacing the aggregates and flooding the aggregates with monomer in place.
The first successful project to incorporate polymer concrete as an industrial floor overlay was performed at the Butler Machinery Company in Fargo, North Dakota. Butler Machinery Company is a regional sales and service company for Caterpillar equipment. As a part of their facilities, Butler has an equipment wash room which is used to clean all equipment coming in for servicing or repairs. This equipment frequently includes large crawler tractors. As a result of the severe, continuous use of this room, extensive erosion of the concrete floor has taken place. Any repairs to the floor would be required to withstand the heavy crawler tractor traffic. The wash room is approximately 20 feet wide and 50 feet long and the existing floor was 8 inches thick. The floor was installed initially in about 1957 and has been worn up to 4 inches in the path of the tractors. A normal concrete floor overlay would not have stood up to these severe conditions. The alternative of removing the remaining floor and replacing it would have been very expensive. In addition, repairs using normal concrete would have required a month long shut down of the facility to properly cure the concrete while the wash room is required daily.
The owner elected to have a polymer concrete overlay installed instead. This choice was dictated by the speed with which the floor could be repaired and put back into service, and the much lower cost of a polymer concrete overlay when compared with an epoxy floor overlay. The wash room was shut down on a Thursday evening and preparation for repairs began Friday morning. The slab was thoroughly cleaned and dried and, following drying, forms were erected in approximately six-foot wide strips to establish the correct floor elevations for drainage slopes and to serve as screed chairs. The first strip of PC was placed Friday evening and the remainder of the floor was completed Saturday. The overlay thickness varied from 3/4 inch near the walls to about 4 inches in the vehicle tracks. The contractor completed placing and finishing Saturday evening and returned Sunday to clean up the work area. Butler Machinery put the wash rack back into service Monday morning. The cost for high strength extremely durable PC floor overlays can be less than half the cost of an equivalent epoxy floor and, when considering the cost of a long shut down, is many times less than a cost of installing a new floor.
Although polymer concrete and polymer impregnated concrete have properties that make them ideally suited to structural restoration and industrial floor applications, these materials also have some characteristics that require their installation by experienced and knowledgeable contractors. The monomers used are potentially toxic and flammable much as gasoline would be if poured out over a large area. The materials also must be handled as would most organic chemicals, with due precautions for potential safety hazards. Further, although creating some additional precautionary requirements, these materials can be custom formulated at the job site for a particular application. This provides leeway in the length of the curing period at various temperatures and the final properties that will be achieved by the concrete. Strict attention to every detail of the installation procedure has to be mandatory. This means that thoroughly trained, experienced contractors are required to perform the placement work. Also, since the material can be custom formulated to suit particular application, detailed individual job specifications prepared by experienced consultants becomes important.
Work completed to date shows that substandard and badly deteriorated concrete in buildings can be repaired using PIC techniques provided the concrete is dry and sufficiently porous to except the monomer readily and that safety precautions are taken to protect workmen and to prevent accidents. In industrial applications such as factory floors, equipment service floors, areas subject to acid deterioration (or other environments hostile to concrete), parking ramps, etc., where concrete is deteriorating more rapidly than is acceptable, polymer concrete is an alternative. The use of polymer concrete as an overlay to provide a waterproof membrane and a high strength, durable wearing surface for traffic requirements can be cost effective. By using PC and PIC techniques in conjunction with other repair and restoration methods available, an expanded technology for repairing concrete structures is possible.
In preparing and contracting restoration of this type, coordination and quality control of construction work require careful monitoring. The contractor chosen should have considerable experience in concrete restoration by conventional means and preferably should perform in situ test work prior to being assigned a contract.
The technology of polymers in concrete has emerged to become a viable, economical material for producing, patching, rehabilitating, protecting and improving concrete. The construction and repair potential of polymer concrete was fully demonstrated as the World Of Concrete IV Exposition in Phoenix, Arizona. The materials have been used successfully and predictably in dams, bridges, precast products and buildings.
Another article on the use of polymers in concrete, this one about a very special polymer impregnated concrete is here.
ACI 548 Committee, American Concrete Institute, Brookhaven National Labs, Composite Fabricators Association, The Yellow Pages, The Hometown
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