Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : High strength concrete

Influence of Minimum Tension Steel Reinforcement on the Behavior of Singly Reinforced Concrete Beams in Flexure

Ali A. Abdulsada; Raid I. Khalel; Kaiss F. Sarsam

Engineering and Technology Journal, 2020, Volume 38, Issue 7, Pages 1034-1046
DOI: 10.30684/etj.v38i7A.902

The requirements of minimum flexural reinforcement in the last decades have been a reason for controversy. The structural behavior of beams in bending is the best way of investigating and evaluating the minimum reinforcement in flexure. For this purpose, twelve singly reinforced concrete beams with a rectangular cross-section of (125 mm) width by (250 mm) height and (1800 mm) length were cast and tested under two-point loads up to failure. These beams were divided into three groups with different compressive strengths (25, 50, and 80 MPa). Each group consists of four beams with different amounts of tension steel reinforcement approximately equal to (0% Asmin, 50% Asmin, 100% Asmin and 150% Asmin), two bar diameters (Ø6 mm and Ø8 mm) were used as the longitudinal tension reinforcement with different yield and ultimate strengths, the minimum amount of reinforcement required is calculated based on ACI 318M-2014 code. The results show that for the reinforced concrete beams, the flexural reinforcement in NSC beams increases the first cracking load and the increment increased with an increasing amount of reinforcement, while for HSC beams the increasing in first cracking load are very little when the quantity of reinforcement less than the minimum flexural reinforcement and increased with the increasing amount above the minimum flexural reinforcement. The equation of ACI 318M-14 code gives adequate minimum flexural reinforcement for NSC and overestimate value for HSC up to (83 MPa), A new formula is proposed for HSC rectangular beams up to (90 MPa) concrete compressive strength by reducing the equation of ACI 318M-14 code for minimum flexural reinforcement by a factor depending on concrete compressive strength.

Experimental study of Circular Short Columns made from Reactive Powder Concrete

Asmaa Ali Ahmad; Faidhi Abdul-Rahman Alkhazraji; Sarah Mohammed Omar

Engineering and Technology Journal, 2016, Volume 34, Issue 9, Pages 1860-1872

This research studies the behavior of reactive powder concrete (RPC) circular short columns with and without steel fibers of different types, as well as change of the reinforcement kinds of lateral (hoops and spiral) and the spacing between them.
The experimental work consist study of fifteen short column specimens having an overall height of 1 m with circular cross-section of 150 mm diameter are loaded at ends with concentric loads. Six of the specimens are cast with the inclusion of steel fibers with aspect ratio of 75(group 1), and six of other specimens are cast with the inclusion of steel fibers with aspect ratio of 100 (group 2),and the other three specimens is without steel fibers, with hybrid steel fibers and high strength concrete. The concrete mix of fiber-reinforced samples contains 1% by volume of steel fibers of variable reinforcement longitudinal and lateral (hoops and spiral reinforcement).
Experimental data for strength, failure mode, lateral, and the ductility were obtained for each test.
The work concluded that the using of steel fibers in RPC was an effective way to prevent spalling of the concrete cover and increase the ductility and the using of high ratio of longitudinal reinforcement delays the pickling of the columns and increase strength.
The ultimate load capacity of RPC columns of spiral lateral reinforcement is greater than the load of RPC columns of tied lateral reinforcement by about 1.25 to 1.35 times for the two groups.

Mechanical Properties of High Strength Concrete Containing Different Cementitious Materials

Hisham K. Ahmed; Oday A. Abd

Engineering and Technology Journal, 2016, Volume 34, Issue 1, Pages 96-110

High strength concrete hasstrength significantly beyond what is used in normal practice. According to American Concrete Institute (ACI), high strength concrete revised the definition to cover mixtures with specified design strength of 55 MPa or more.
The main objective of this investigation isto study the effect of using different supplementary cementitious materials in binary blends on mechanical properties of high strength concrete.
The experimental work includes threestages: firstly, preparation of cementitious materials (metakaolin and pumice) from local materials,second involves conducting several trial mixes to choose the best of superplasticizer that satisfies the required properties and to specify the optimum water content which is designed in laboratory by 0.3 W/Cm ratio, to achieve workability with (60-80mm) slump and the best compressive strength which was 64.6 at 28 days.
Thirdly carrying out tests to find out the compressive strength, splitting tensile strength, modulus of rupture, on binary concretes including mixes containing silica fume as cement replacement at percentages of 8%, 10% and 15%, mixes containing metakaolin as cement replacement levels of 10%, 15%, and20% and mixes containing pumice at cement replacement of 10%, 15%, and 20%.These properieswere measured at ages ranging from7days to 180 days.
The resultsindicate that the silica fume performs better than other supplementary cementitious materials(metakaolin or pumice) in terms of the compressive strength, splitting tensile strength and modulus of rupture development at ages of 7,28,60,90and180 days where the average percentage of increase when using 8%,10% and 15% ofsilica fume was about(19%,23% and 18.7%) ,respectively, while when using 10%,15% and 20%metakaolin the average percentage of increase was (10%,12.6% and 4%) respectively, also when using 10%,15% and 20% of pumice the average percentage of increase was (2.6%, 6% and 1.5%), respectively.