Chapter 3: Investigation Program
3.1 Materials
The materials used in the experimental phase of this thesis were the typical concrete ingredients including OPC, aggregates, water, and admixtures. Besides, the addition of SSA as a partial replacement of cement. The properties of the constituent materials are given in the following sections.
3.1.1 Aggregate
The passing ability of SCC mixtures mainly depends on the nominal maximum size of the used aggregates. ACI 237R-07 (2008) recommends that the nominal maximum size of the aggregate must be one size less than that suggested by ACI 301 (1989). Hence, from Table 7, and according to the range of cementitious material
content used for the concrete mixtures in this thesis, the maximum aggregate size to be used was 9.5 mm. The inter-particle friction between the coarse aggregate leads to a reduction in the flowability of the mixture and since SCC mixtures needs to be flowable, the ratio of fine to coarse aggregates was increased. According to EFNARC (2005) specifications, the maximum size of coarse aggregate should be less than 12 mm to improve the passing ability of the mixtures by avoiding blocking. Besides, the usage of larger aggregate sizes will o decrease the resistance of segregation of the mix, since it can be separated easily from smaller particles and the paste content.
The types of aggregates used in this study are shown in Figure 23. Coarse aggregate was a crushed natural dolomite from Ras Al Khaima (UAE) with nominal size of 9.5 mm (3/8 in.), a specific gravity of 2.67, and water absorption of 0.7%. Two types of fine aggregate were used; crushed natural stone sand from Ras Al Khaima (UAE) with fineness modulus of 3.72 and specific gravity 2.64, and dune sand from Al Ain area (UAE) with fineness modulus of 0.9 and specific gravity 2.63. Sieve analysis was conducted on all aggregates used, and the results are presented in Table 8.
Table 7: Recommended maximum aggregate size (ACI 237R-07).
Nominal maximum size (mm)
Cementitious material content (kg/m3)
37.5 280 to 330
25 310 to 360
19 320 to 375
12.5 350 to 405
9.5 360 to 415
(a) (b) (c)
Figure 23: Aggregates used in the SCC mixture design. (a) coarse aggregate (9.5 mm), (b) crushed natural stone sand, and (c) dune sand.
Table 8: Aggregate sieve analysis.
Sieve size (mm)
Cumulative Passing % Coarse Aggregate
(10 mm)
Fine Aggregate (Crushed Sand)
Fine Aggregate (Dune Sand)
37.5 100 - -
19 99.96 - -
9.5 99.86 - -
4.75 89.61 95.1 100
2.36 8.12 62 100
1.18 - 35.1 100
0.600 - 19.9 99.7
0.300 - 10.9 99.1
0.150 - 5.1 13.1
3.1.2 Cement
Cement is the main ingredient in the mixture design of SCC. OPC which conforms to ASTM C150 (2019) Type 1 and BS EN 197 (2011) CEM I was used.
According to the manufacturer data sheet, the cement’s specific surface area is 380 m2/kg with specific gravity equal to 3.15 as per the manufacturer data sheet. Chemical composition of the used cement is presented in Table 9 as determined by X-ray fluorescence (XRF).
Table 9: Chemical composition of OPC.
Compound (%)
CaO 73.08
SiO2 15.01
Fe2O3 4.25
MgO 4.25
SO3 4.10
Al2O3 1.97
Equiv. Na2O 0.59 Loss on Ignition 1.60 Insoluble Residue 0.90
3.1.3 Water
Potable water confirming to ASTM C1602 (2006) was used in mixing and curing all the SCC mixtures. This is to ensure that the water is reasonably free from such impurities as suspended solids, organic matter and dissolved salts, which may adversely affect the properties of the concrete.
3.1.4 Sewage Sludge Ash
Municipal sewage sludge utilized in this study was collected from Al Saad Wastewater Treatment Plant (WWTP) in Al Ain, UAE. Raw sewage sludge was homogenized and stored into labeled containers. The delivered raw sewage sludge had 8.38% moisture content. Sewage sludge was incinerated using a programmable electrical furnace at three different temperatures and for three different periods as summarized in Table 10. As shown in Figure 24, a change in the SSA particles color
was observed when the temperature was raised from 700oC to 1100oC. The produced granular particles of the incinerated SSA particles were ground using a disc-type grinder to reduce particle size and increase its fineness and were placed in tightly sealed containers to prevent contact with any source of moisture. A total of nine samples of finely ground SSA were obtained. After incineration, the SSA water absorption for all the particles was about 60%. Further characterization of SSA will be discussed in detail in Chapter 4. Figure 25 represents the disc- type grinder used for grinding, and the ground SSA particles.
Table 10: Incineration temperature and time for sewage sludge samples.
Sample I.D. Incineration Temp.
(oC)
Incineration Duration (hr)
RSS Raw sewage sludge
SSA7-2 700 2
SSA9-2 900 2
SSA11-2 1100 2
SSA7-4 700 4
SSA9-4 900 4
SSA11-4 1100 4
SSA7-6 700 6
SSA9-6 900 6
SSA11-6 1100 6
Figure 24: Incinerated SSA particles before grinding.
(a) (b)
Figure 25: SSA grinding. (a) Disc-type grinder, and (b) ground SSA.
3.1.5 Admixtures
In this thesis, in order to produce a SCC mixture, two types of admixtures were used namely: Superplasticizer (SP) and viscosity modifying admixtures (VMA). Both types were obtained from the chemical company BASF. As recommended, prior of using admixtures in the mixture, the admixtures were mixed with the mixing water.
The optimum dosage of these admixtures for yielding the best fresh properties was determined based on trial mixtures. Both types are supplied in the form of a liquid, water soluble compounds. A polycarboxylic ether-based SP (Glenium® sky 504) which conforms to Type G in ASTM C494 (2013) and Type 2 in ASTM C1107 (2012) was used in the study. The amount used varied from 1.6% to 2.4% by weight of the binder content. A high molecular weight synthetic co-polymer VMA (RheoMATRIX
® 110) was used in the preparation of the SCC mixtures studied in this thesis. The dosage varied from 0.35% to 0.6% by weight of the binder content. The properties of the used SP and VMA were provided by the manufacturer and are illustrated in Table 11.
Table 11: Typical properties of chemical admixtures as obtained from supplier.
(Manufacturer’s datasheet).
Superplasticizer Viscosity modifying admixture
Appearance Whitish to straw colored
liquid Brownish liquid
Specific gravity 1.115 at 25oC 1.010 g/cm3 Chloride content “chloride free” to EN 934-2 <0.1%
Alkali content (as
NaO equivalent) 0.26% -