Mechanical Properties of Calcium Aluminate Cement Reinforced with Plasma-Treated Basalt Fibers for In Situ Combustion

Brittleness and poor tensile/flexural properties restrict the application of calcium aluminate cement (CAC) in oil and gas wells. Reinforcing CAC with fibers is an effective method for improving its strength and toughness and overcoming the shortcomings of its mechanical properties. In this article, as an auxiliary cementing material, slag does not affect the thickening time of CAC. After adding slag, the cement slurry meets the thickening time during cementing construction, and basalt fiber is selected as the toughening material. The enhancement effect of basalt fiber on the mechanical properties of CAC slag composites is studied, including the evaluation of the macroscopic mechanical properties and microstructure at a high temperature (500 °C). The optimum composition of basalt and fiber-reinforced CAC was determined. Basalt fibers were added to CAC at different contents of 0, 0.1, 0.2, 0.3, 0.4, and 0.5% based on the weight of the cement. All the results showed that the introduction of basalt fibers could significantly enhance the strength of the cement at high temperatures. Compared with the control samples, an additional increase in the compressive and tensile strengths of the samples of 35.1 and 85.2%, respectively, was achieved at high temperature with approximately 0.4% fiber content. Plasma treatment further improved the reinforcing effect of the basalt fibers, where the high-temperature compressive and tensile strengths of the samples increased from 28.88 and 1.52 to 35.23 and 1.87 MPa, respectively, an increase of 21.98 and 20.6%, respectively, compared with the untreated basalt fibers. When the cement paste is cured by simulated curing for 28 d, the high-temperature compressive strength and tensile strength with plasma modification increased from 28.26 and 1.5 to 29.1 and 2.15 MPa, respectively, an increase of 3.0 and 43.3%, respectively. The structure of the formed hydrates was studied using scanning electron microscopy. Furthermore, toughening of the basalt fiber-reinforced CAC-based composites resulted mainly from crack bridging and fiber pull-out.