الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 153 |  |  |
| | | from | 153 | | |
Abstract
-Recently, concrete admixtures are widely used as the main constituent in high performance concrete (HPC), which used in, tall structures and bridges.
The concrete admixtures have the following advantages:
The superplasticizers used to reduce the mixing water of concrete with maintaining its workability and subsequently increase its durability, or
- Increase the workability of concrete to be easy used and easy molded without vibrating with maintaining its durability, or
Reduce the cement and water content of the concrete with maintaining its compressive strength.
-The concrete admixtures are inorganic or organic materials in a solid or liquid state added to the normal components of the mix, in most cases up to a maximum of (5%) by weight of the cement or cementitious materials.
-The most important admixtures are ones added to accelerate (called accelerators), retard (called retarders) the setting or the hardening or decrease the mixing water (called water reducers) needed to obtain a given degree of workability, conventional water reducers allow W/C ratio to be decreased by (5 — 15 %).
More powerful water reducers, called superplasticizers (SPs), they decrease the W/C ratio up to (30 %) without excessive retardation,
excessive air entrainment or flash setting, which also called high range water reducer (HRWR).
One key for successful preparation of high performance concrete (HPC) is the addition of proper superplasticizer, such as lignin sulphonate (LS), naphthalene sulphonate formaldehyde (NSF), melamine sulphonate formaldehyde (MSF) and the recently one is the poly carboxylate (PC).
In this study two new categories have been synthesized through different methods. One of them is water soluble phenol sulphonate formaldehyde (PSF), which synthesized through three different methods and the other is sodium sulfanilate - phenol formaldehyde copolymer (SSPF), which synthesized through two different methods.
These five prepared superplasticizers and commercial one [Mt.] were admixed [in different dosages (0.0, 0.25, 0.5, 0.75, 1.00, 1.5 and 2.0 mass %) of cement] with OPC and SRC pastes.
The effect of these admixtures on the properties of these cement pastes was investigated through the following :
a.Rheological properties including, shear stress — shear rate, yield stress, plastic viscosity and mini-slump of these pastes.
b.Rate of hydration including chemically combined water contents and gel/space ratios.
c.Mechanical properties mainly the compressive strength.
from the results obtained the following conclusions could be derived:
1. Additions of prepared and commercial superplasticizers to cement pastes reduce their values of shear stress, yield stress and plastic viscosity.
The maximum values of shear stress of OPC pastes admixed with 1% of SPs were 703.4, 623.5, 371.8, 609.8, 589.2 and 257.4 Pa. Meanwhile, the values of yield stress were 90.6, 68.6, 64.0, 67.5, 72.5 and 65.8 Pa. In addition, the values of the plastic viscosity were 6.9, 6.6, 3.4, 9.1, 5.7 and 2.1 Pa s for Mt., A, B, C, D and E, respectively.
2.Additions of prepared and commercial SPs to cement pastes increase their mini-slump.
The values of mini-slump of OPC pastes admixed with 1% of SPs were 8.4, 8.1, 8.0, 8.1, 8.0 and 8.2 cm for Mt., A, B, C, D and E, respectively.
3.Addition of the prepared and commercial SPs reduces the water of consistency of cement pastes as the following:
Addition of (0.25) cement mass % of these polymers reduce mixing water by (9.6, 5.6, 4.4, 5.6, 4.4 and 7.2%). Meanwhile, addition of (0.50%) of these polymers reduces mixing water by (14.4, 10.8, 8.4, 10.8, 8.4 and 10.8%). And addition of (1.00%) of these polymers reduce mixing water by (21.6, 18.4, 17.6, 18.4, 17.6 and 19.6%), for Mt., A, B, C, D and E, respectively.
4.The chemically combined water contents of cement pastes admixed with (0.00, 0.25, 0.50 and 1.00%) of commercial Mt. were (11.03, 11.16 and 11.23%), (8.50, 9.54 and 10.52%), (7.25, 8.82 and 9.50%) and (6.91, 7.40 and 8.46 %). While those admixed with ( 0.25, 0.50 and 1.00 %) of polymer B were ( 8.69, 9.84 and 11.20 %), ( 7.64, 9.10 and 9.54 %) and ( 7.15, 7.89 and 8.82 %) for curing time of ( 3, 7 and 28 days), respectively.
5.It is found that; the compressive strength increases with increasing the curing time.
Due to increase the hydrated phases which decrease the porosity of the cement paste and as the dosages of the polymers increase the compressive
strength increase as the result of reduce the mixing water which decreases the initial porosity of the cement pastes.
The increase in the compressive strength of cement pastes admixed with (0.25, 0.50 and 1.00%) of Mt. and hydrated up to 28 days were (76, 82.4 and 106.4%) at 3 days, (36.6, 38.4 and 49.1%) at 7 days and (36.5, 38.3 and 41.5%) at 28 days, respectively.
While those admixed with (0.25, 0.50 and 1.00%) of polymer B and hydrated up to 28 days were (68.2, 93.1 and 96.0%) for 3 days, (27.4, 37.0 and 47.5%) at 7 days and (21.7, 34.4 and 36.2%) at 28 days, respectively. 6. The above results confirmed by gel/space ratios.
where the gel/ space ratio increases with increasing the hydration time, due to increase the hydrated products which decrease the porosities of the paste, while gel/ space ratio decrease with increase the dosages of admixture due to decreases the initial porosity of the cement pastes as a result of reduce the mixing water.