CONSTRUCTION MATERIALS

Construction Materials

Construction Materials

Introduction

Shrinkage of Concrete

Shrinkage of concrete exposed to dry environment is an important characteristic, and it may cause cracking if the concrete element is restrained [Zhang 2005].

The main factors that affect the magnitude of drying shrinkage in concrete include the cement fineness and content, the aggregate size and content, the W/C ratio, curing period, the relative humidity and the member size. The aggregate used in the concrete mixture acts to restrain the shrinkage of cement paste. Concrete with a higher aggregate content has less shrinkage than that of lower aggregate content. Aggregate with a higher modulus of elasticity or rougher surface has more resistant to shrinkage. In general, a higher water-to- cement (W/C) ratio will produce greater drying shrinkage. [Mokarem 2002].

Self- Compacting Concrete.

The concept of self-compacting concrete (SCC) was proposed in 1986 by professor Hajime okamura (1997), but the prototype was first developed in 1988 in Japan, by professor ozawa 1989 at the university of Tokyo [Okamura and Hajimar 1997 , Ozawa 1989] . SCC describes a concrete with the ability to compact itself only by means of its own weight without the requirement of vibration . This new concrete was deliberately designed to be able to fill every corner of the form and encapsulate all reinforcement with maintained stability only under the influence of gravitational forces, without segregation or bleeding. This makes SCC particularly useful wherever placing is difficult, such as in heavily-reinforced concrete members or in complicated work forms-to fulfill nation request, concrete need to has special properties in fresh state. On the other hand, the flow ability of concrete has to avoid segregation. These properties of the fresh concrete can be realized by high enough mix design, a proportion of aggregate is replaced by powder material while the water contents is kept constant [M.A. Ahmadim et . al]. [Jianxin and Holger 2002] concluded that the application of new super -plasticizers and powders in a high performance concrete gives opportunity to produce SCC that reaches very high compressive strength. These concretes show a very good workability in the fresh state, also the hardened concrete shows excellent quality .

Experimental Program

To determine the workability, different test methods are adopted such as slump-flow, T50cm, L.box, U-box and V-funnel. The mechanical properties studied are, compressive strength, splitting tensile strength, free and end restrained shrinkage. Table (1) shows the mix proportions by weight for normal concrete and self-compacting concrete in this work.

Table (1):Mix proportions by weight

Materials

Normal concrete mix

Self-compacting concrete mix

Cement (kg/M3)

450

450

Filler (kg/M3)

-

65

Fine aggregate (kg/M3)

750

750

Coarse aggregate (kg/M3)

790

790

SP (Liter/100 kg cement)

-

2

W/P

0.45

0.45

W/C

0.51

0.51

Materials

1. Cement

Ordinary Portland Cement (O.P.C) manufactured by united cement company , commercially known [TASLUJA - BAZIAN] was used throughout this investigation. This cement complied with the Iraqi specification No. 5: 1984. The chemical composition and physical properties are presented in Tables (2) and (3).

2. Fine Aggregate

Natural sand from AL-Akaidur region was used. The result of physical and chemical properties of the sand are listed in Table (4). Its grading is conformed to the IQS ...