The compressive characteristics of the steel-slag concrete were investigated through an experimental test. The term “steel-slag concrete” in this research work was defined as a kind of concrete using steel-slag material as a coarse aggregate replacement. Three types of the steel-slag concretes were examined under compression as follows: XT01, XT02, XT03 with their cement/water ratios of 1.76, 2.00, 2.21, respectively. The coarse aggregate used in producing concrete was steel-slag material, while the fine aggregate was traditional river sand; the ratio of coarse aggregate to fine aggregate was kept constant at a value of 1.98. Firstly, the age-dependent compressive strength of the steel-slag concretes were investigated up to one year; it was clear that the concrete strength increased rapidly in 7 days, then more and more slowly after that. Secondly, the modulus of elasticity and Poisson’s ratio of the steel-slag concretes were explored at the 28-day age. Thirdly, there was an important size and shape effect on the compressive strength of the XT02, and its significance of brittleness in failure was analytically analyzed. Lastly, the effects of water amount added in the XT02 on its compressive strength and slump were evaluated at the 28-day age.

Experimental tests were performed to investigate the responses of coarse steel slag concrete under splitting and flexure. The name of coarse steel slag concrete (CSC) here refers to concrete using industrial byproduct steel slag as natural coarse aggregate replacement. Three CSC types were examined in this investigation as follows: CSC1, CSC2, and CSC3, having a water/cement ratio of 0.57, 0.50, and 0.45, respectively. In the compositions of the three studied CSCs, the water content by weight remained constant and other partial materials were changed, but the ratio of coarse steel slag/fine river sand was still fixed. Under splitting, three types of test methods were conducted including a cylinder splitting test, side-cube splitting test, and diagonal-cube splitting with the same sizes: the diameter of the cylinder and side of the cube were 100 mm. The orders of splitting test methods were observed for CSC2 as follows: cylinder > side-cube > diagonal-cube in terms of maximum applied load, and, cylinder > diagonal-cube > side-cube in terms of splitting strength. Additionally, there were clear size effects on the splitting strengths of CSC2 with different sizes as follows: 70 mm, 100 mm, 150 mm for cylindrical diameter, and/or cubic side. Under flexure, there was a strong co-relationship between compressive strength and flexural resistance of CSCs. The flexural engineering parameters were examined then assessed for plain CSCs, using a rectangular prism with the size of 100 × 100 × 300 mm (width × height × span-length), and, for steel-reinforced beams using CSCs with the size of 200 × 300 × 3000 mm (width × height × span-length).

Xỉ thép là sản phẩm phụ, được tạo ra trong quá trình luyện thép. Theo thống kê của Sở Tài nguyên-Môi trường (2017), tại Bà Rịa Vũng Tàu có 6 nhà máy thép đang hoạt động với tổng công suất 4,5 triệu tấn/năm và lượng xỉ thép phát sinh vào khoảng 10% sản lượng thép, phần lớn đang được lưu trữ và là nguyên nhân gây tác động xấu đến môi trường. Trong nghiên cứu này, cấp phối hạt của xỉ thép được điều chỉnh bằng cách phối trộn với cát mịn tạo thành cấp phối xỉ thép-cát mịn (tỷ lệ xỉ thép/cát mịn là 80%/20%), sau đó gia cố với xi măng với hàm lượng 4%, 6%, 8%. Các thí nghiệm xác định cường độ chịu nén, cường độ chịu ép chẻ và mô đun đàn hồi ở tuổi 7, 14, 28 và 56 ngày được thực hiện để đánh giá khả năng làm việc của vật liệu gia cố trong kết cấu áo đường. Kết quả cho thấy các đặc tính kỹ thuật của cấp phối xỉ thép-cát mịn gia cố xi măng được cải thiện đáng kể nên có thể dùng làm lớp móng trên của kết cấu áo đường khi hàm lượng xi măng gia cố từ 6-8%. Từ khóa: xỉ thép; cát mịn; gia cố xi măng; cường độ chịu nén; cường độ chịu ép chẻ; mô đun đàn hồi.