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ABSTRACT Service environments for piping used in geothermal applications are chemically and physically complex and typically aggressive. In some geothermal power plants, cement mortar linings are applied to provide corrosion protection to steel pipes used for transportation of geothermal fluids back to the reservoir. However, the linings are susceptible to deterioration and have a finite life. Research was undertaken to improve the durability of cementitious linings and thereby increase the service life of lined pipes. Samples of mortar were exposed to simulated hypersaline geothermal brine at elevated temperature. The mortar mix proportions and chemistry were varied and the performance and properties compared. Latex modification of the mortar was also explored. This paper describes the results of preliminary testing and provides recommendations on improvements in cement mortar formulations.
Kessler, R.J. (Florida Department of Transportation) | Powers, R.G. (Florida Department of Transportation) | Paredes, M.A. (Florida Department of Transportation) | Sagüés, A.A. (University of South Florida) | Virmani, Y.P. (Federal Highway Administration)
Laboratory and field evaluations are ongoing on several commercially available corrosion inhibiting admixtures for concrete. The study, presently in its tenth year focuses on long-term performance in partially submerged coastal marine applications. The study includes laboratory and field evaluations to determine the ability of the inhibitors to remain stable over long periods of time, determinations of long-term effectiveness of corrosion inhibiting capabilities and a tentative quantitative assessment of durability improvements and possible negative side effects.
Corrosion Inhibitors for concrete have been in use for several decades to minimize the corrosion of rebar embedded in concrete. While there are several corrosion inhibitors available in the market place, not all of them have proven useful or cost effective. Calcium nitrite1, 2 is the only concrete corrosion inhibitor with a clear documented, long-term history of performance in ordinary Portland cement concrete (OPCC).
The present project examines the corrosion performance of three familiar concrete corrosion inhibitors in OPCC and HPC. The purpose of the project is to evaluate the effect of the presence of each type of inhibitor and its dosage on the onset and progression of corrosion in concrete. During the design phase of the project, special emphasis was given to establishing the critical chloride concentrations for corrosion initiation for each inhibitor, as a function of concrete mix parameters. This information is instrumental in life-cycle analyses and consequently for efficiently budgeting construction and maintenance costs. The critical chloride concentrations are to be obtained by incorporating information from non-destructive electrochemical testing and detailed autopsy analysis of the low permeability mixes.
The University of South Florida and the Florida Department of Transportation are performing the present research study jointly as a multi-year effort to evaluate the performance of concrete with various corrosion inhibitors combined with pozzolanic admixtures. The present paper details research findings during the first ten years of the project.
A summary of the mix proportions used is given in Table 1. All mixes used 985 kg/m3 (1657 lbs/yd3) coarse aggregate with a maximum diameter of 12 mm (0.5 inches.) The coarse aggregate was oolitic limestone unless otherwise indicated; granite coarse aggregate was used in one group to investigate the role of coarse aggregate on corrosion. The fine aggregate was silica sand with a fineness modulus of 2.16. The cementitious factor was 7 bags (390 kg/m3, 657 Lbs/yd3) using AASHTO type II Portland cement with 0.41 and 0.5 water to cementitious ratios. The minimum design strength for the 0.41 W/C concrete was 38 MPa (5500 psi,) while for 0.50 W/C was of 28 MPa (4000 psi.) Pozzolans were used as a replacement at a replacement rate of 20% by weight for AASHTO Type F fly ash and 8% by weight for Silica Fume. The same air entrainer and water reducer was used in all mixes at a nominal rate. Concrete slump was controlled by the addition of superplasticizer with a target of 75 mm (3 inches) for the 38 MPa concrete and 200 mm (8 inches) for the 28 MPa concrete.
Abstract Nanotechnology encompasses a wide scope of disciplines and nanomaterials are now being used as commercially viable solutions to technical challenges in industries ranging from electronics to bio-medicine. Recently, the application of nanomaterials to solve problems in oilwell cementing has begun to be investigated by several different research groups in the oil and gas industry. The following uses of nanomaterials have been presented by several independent laboratories as possibilities in the oilwell cementing industry: (1) nanosilica and nanoalumina as potential accelerators; (2) nanomaterials including carbon nanotubes (CNTs) with high aspect ratio to enhance mechanical properties; (3) nanomaterials to reduce permeability/porosity; and (4) nanomaterials to increase thermal and/or electrical conductivity. In this paper, a review of the aforementioned application concepts is presented with a focus on understanding the role of multiwall CNTs (MWNTs), nanosilica, and nanoalumina in oilwell cement hydration chemistry. The influence of the integration of MWNTs into oilwell cement on the physical properties of cement is discussed. Results from an isothermal microcalorimetric study are presented to help understand the difference between the mode of acceleration of a typical cement accelerator, like CaCl2, compared to nanosilica and/or nanoalumina.