BEHAVIOR OF LAP SPLICES IN REINFORCED CONCRETE BEAMS USING RECYCLED CONCRETE COARSE AGGREGATE

Abstract

Abstract As a matter of fact, the issue of concrete and demolition waste disposal represents a serious problem in the civil engineering work since it is accumulated in large quantities in some countries like Iraq. Using of such materials in new construction after grinding is considered a good sustainable and cost effective solution to this concern. The basic aim of this study is to investigate the behavior of lap splice when recycled coarse aggregate is used in structural members by experimental program. This program comprises the investigation and assessment to the bond stress lab splices by using 12 beam splice specimens of 250 x 350 x 2500 mm dimensions under the application of two point loads and 18 direct pull out test specimens. Two mix designs are proposed with nominal 20 and 30 MPa compressive strength, more precisely, the degree of coarse recycled aggregate partial replacement ratio taken throughout this study as 0 %, 50 % and 100 % respectively using a crushed concrete casted originally using the same mixes defined. In addition, the beam splice specimens were devoted to investigate lap splice bond strength in both singly and doubly beams to account the desired behavior in tension and compression into consideration. II The results showed that an increasing the degree of RCA with 50% and 100% replacement decreases the ultimate load of the singly beam specimens in case of 20 MPa compressive strength by about 6% and 10%, while 3% and 8%, respectively in doubly beam specimens. In case of 30 MPa compressive strength the decreasing in ultimate load became by about 4 and 10% for singly beam specimens, 1 and 4% in doubly beam specimens, respectively. Furthermore, increasing the degree of RCA by 50 and 100% decreases the consequent first crack load in case of singly beam specimens in 20 MPa compressive strength by 17 and 25%, while in doubly beam by about 17 and 23%, respectively. In case of 30 MPa compressive strength the decreasing in first crack load became by about 20 and 27% for singly beam specimens and 7 and 20% in doubly beam specimens. The results also showed that replacing 50% of coarse aggregate decreases the bond stress by 2.63 to 6.25 % in singly beam specimens and 3.23 to 7.76 % in doubly beam specimens while replacing 100 % decreases such stress 5.26 to 10.42 % in singly beam specimens and 5.65 to 11.42 % in doubly beam specimens. In addition, compressive strength, modulus of elasticity, splitting tensile strength, workability and modulus of rapture have also decreased when degree of recycled coarse aggregate is increased. In other hand, the brittle failure behavior is evident in the entire beam specimens that conducted throughout this study. Finally, the direct pull out test specimens results showed that the bond stress is generally decreased by the increase of the degree of recycled coarse aggregate for high compressive strength while this does not exist clearly in low compressive strength