Behavior of structural lightweight concrete produced with expanded clay aggregate and after exposure to high temperatures

The residual compressive strength of eight lightweight concrete mixtures containing three commercial grading (Liapor HD 5 N, Liapor HD 7 N, and Liapor 8F) of coarse lightweight aggregate (LWA) were determined after to expose at high temperatures. Eight mixes were produced, two by normal weight aggregate and the rest by different types of LWA. The produced concrete was analyzed after high temperature exposure and the effect of using LWA, the type of LWA, and compaction method was studied. To do so, visual inspection, residual compressive strength, crack pattern, spalling, and thermoanalytical analysis were conducted. Generally, it could be concluded that concrete formulations with LWA behave more advantageous up to 500 °C, compared to those with quartz gravel aggregates. Moreover, this study found that an ideal type of LWA to produce structural concrete was Liapor HD 5 N, which was used for producing the mixes L1 and L3.

IMPLEMENTATION OF FELDSPAR AS PARTIALLY REPLACEMENT MATERIAL IN CEMENT MORTAR (EXPLORATION AND APPLICATION)

This paper aims to explore and evaluate the use of Jordanian Feldspar as a natural resource partially replacement material for each of cement and sand in cement mortar. First, Al-Jaishia area was explored through a global positioning system (GPS) navigation to gather site samples of Feldspar raw material. Afterward, cement and sand were partially replaced by Feldspar with substitution ratios of 5%, 10%, 15%, 20%, and 25% for each. The study included the effect of cement replacement on normal consistency and setting time for cement paste. The water content along with initial and final setting times increased via the increment of cement replacement ratio. Moreover, mechanical properties (compressive, flexural, and residual compressive strengths) of cement mortar due to both cement and sand replacement were evaluated. The compressive and flexural strengths after 3, 7, and 28 days of curing were examined for both cement and sand replacement. While, residual compressive strength for cement replacement after 28 days was measured at elevated temperatures of 400°C, 600°C, and 800°C. The compressive and flexural strengths decreased by increasing the Feldspar replacement ratio for both cement and sand at all specimen ages. Whereas, heat resistance properties were improved by cement/Feldspar replacement. The best result for residual compressive strength was obtained at 15% replacement ratio and 400°C temperature.

Effect of Quarry Rock Dust as a Binder on the Properties of Fly Ash and Slag-Based Geopolymer Concrete Exposed to Ambient and Elevated Temperatures

This study presents the performance of quarry rock dust (QRD) incorporated fly ash (FA) and slag (SG) based geopolymer concretes (QFS-GPC) exposed to ambient and elevated temperatures. A total of five QFS-GPC mix types were prepared. The quantity of FA (50%) was kept constant in all the mixes, and SG was replaced by 5%, 10%, 15%, and 20% of QRD. The fresh, hardened properties of the QFS-GPC mixes, viz., workability, compressive strength, splitting tensile strength, and flexural strengths, and XRD for identification of reaction phases were evaluated. The prepared mixes were also heated up to 800 °C to evaluate the residual compressive strength and weight loss. The workability of the QFS-GPC mixes was observed to be reduced by increasing the dosage (0 to 20%) of QRD. Superplasticizer (SP) was used to maintain the medium standard of workability. The compressive, tensile, and flexural strengths were increased by replacing SG with QRD up to 15%, whereas a further higher dosage (20%) of QRD reduced the mechanical strengths of the QFS-GPC mixes. The strength of the QFS-GPC specimens, heated to elevated temperatures up to 800 °C, was reduced persistently with the increased contents of QRD from 0 to 20%. It was concluded from the study that QFS-GPC can be used to achieve 30 MPa strength of concrete.

Effects of Elevated Temperatures on the Properties of High Strength Cement Paste Containing Silica Fume

High strength concrete (HSC) production is worldwide increased and gradually replacing the normal strength concrete (NSC). The cement matrix of concrete is the essential part that governs the behavior and strength of concrete. Several researchers have focused on the performance of hardened cement paste (HCP) at ambient temperature such as using different types of supplementary cementitious materials (SCM). However, the performance of HCP after exposure to elevated temperatures requires further evaluation. The present study investigates the influence of different replacements of silica fume (SF) to cement and different water/binder ratios (w/b) on the compressive strength of HCP before and after exposure to elevated temperatures. Eighteen mixes have been prepared and tested. Results of compressive strength tests at ambient temperature were ranged from 58 to 102 MPa depending on the difference of w/b. Furthermore, a new method has been adopted for comparing the responses of HCP at elevated temperatures "heat endurance". Results showed that using SF enhances the residual compressive strength of HCP after exposure to elevated temperatures due to the pozzolanic reaction and the filler contribution. Mixes containing 6%, 12%, and 15% of SF have shown the highest relative residual compressive strength values for 0.30, 0.35, and 0.40 w/b, respectively. Consequently, the results were significantly affected by changing the w/b ratio. Finally, different measurement techniques were provided to support the work, including Thermo-Gravimetric (TG), Computed Tomography (CT), and Scanning Electron Microscope (SEM) analysis to characterize the loss of mass, porosity, and micro-structure alteration of HCP.

Behavior of Biochar-Modified Cementitious Composites Exposed to High Temperatures

In this study, the effect of biochar on the high temperature resistance of cementitious paste was investigated using multiple experimental methods. The weight loss, cracks, residual compressive strength, and ultrasonic pulse velocity (UPV) of biochar cementitious paste with 2% and 5% biochar exposed to 300, 550 and 900 °C were measured. The products and microstructures of biochar cementitious paste exposed to high temperatures were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The results showed that the cracks of specimens exposed to high temperatures decreased with increasing biochar content. The addition of 2% and 5% biochar increased the residual compressive strength of the specimens exposed to 300 °C and the relative residual compressive strength at 550 °C. As the exposure temperature increased, the addition of biochar compensated for the decreasing ultrasonic pulse velocity. The addition of biochar contributed to the release of free water and bound water, and reduced the vapor pressure of the specimen. The addition of biochar did not change the types of functional groups and crystalline phases of the products of cementitious materials exposed to high temperatures. Biochar particles were difficult to observe at 900 °C in scanning electron microscopy images. In summary, because biochar has internal pores, it can improve the high-temperature resistance of cement paste.