الفهرس 
INTRODUCTION AND OBJECT OF INVESTIGATIONOnly 14 pages are availabe for public view
 |  | from | 255 |  |  |
| | | from | 255 | | |
Abstract
CHAPTER (IV)
SUMMARY AND CONCLUSION
Grinding aids are organic substances that are strongly adsorbed on the surface of ground particles, so that preventing agglomeration and coating on ball and mill lining. The main purposes for their addition are increasing the grindability of the cement clinker and therefore reduce the energy required to grind the clinker into a given fineness. As a consequence the presence of grinding aids increases the efficiency of the cement mill. Grinding aids have been used for more than 50 years and the most common additives can be divided into groups according to their structure as glycols, alcohols, amines and phenol type compounds.
In addition to increase the efficiency of the mill, some grinding aids also provide important positive effects on the final cement such as increasing rheology of the fresh cement paste or concrete and improvement of the strength development. Grinding aids that provides these properties are called “quality improvers” or “performance enhancer. The addition of grinding aids to the clinker during cement production is indeed important for several reasons. Firstly, fineness (Blaine) of the finished cement is one of the main factors that are affecting the development of early strength. Besides, addition of grinding aids provides a decrease in energy which consumed during cement grinding. Their main goals are to reduce energy required to grind clinker in this fineness and therefore increase efficiency of cement mill.
In this study, the effect of some grinding aids on the properties of dry and hydrated ordinary Portland cement in absence and presence of limestone was investigated. The dry mixtures. Partial replacement of OPC by different ratios of limestone (5 & 10 wt. %) was carried out. The weight of each dry mix was 2 Kg that homogenized and grinded for 45 minutes in “Lab Bond Ball Mill” in absence and presence of grinding aids. Grinding aids used in this study were propylene glycol (PG), ethylene glycol (EG), triethanol amine (TEA) and commercial grinding aid (CG). The ratios of grinding aids added were 0.03, 0.04 and 0.05 wt. % with respect to the dry cement.
Each dry cement mix whether with or without GAs addition was mixed with the required amount of water to give desired standard consistency. Then, the setting (initial and final) times of cement paste of each mix was measured using Vicate needle device. The compressive strength of the cement mixes was measured using mortar having composition (1.0: 0.5: 3.0) of cement: water: standard sand ratios and mixed using automatic mixer. The freshly prepared mortar was placed in stainless steel moulds with dimensions (40×40×160 mm) after removing of air bubbles using jolting apparatus. After molding, the moulds were kept inside humidity cabinet at 95±3 % RH for 24 hours at 20±1 º C. After 24 hours the specimens were demoulded and cured in tap water for the hydration ages; 2, 7, 28 and 90 days. The following tests were carried out:
1. The compressive strength values were measured using a hydraulic test machine.
2. Hydration kinetics via determination of chemically combined water and free lime.
3. Determination of phase composition and microstructure via the following examinations; X-ray diffraction analysis (XRD), differential thermal analysis (DTA) and Scanning Electron Microscope (SEM) for some selected samples were carried out to investigate the morphology and phase composition of the formed hydration products.
The main results obtained from this study can be summarized as follows:
A. OPC admixed with propylene glycol (PG) and commercial grinding aids (CG).
i) Higher values of Blaine area were observed for OPC mixtures admixed with PG and CG than that of OPC control; a remarkable increase of grindability index and consequently water of consistency with PG more than CG at most doses applied, while lower values of initial and final setting times with using PG and CG than OPC control.
ii) The OPC mixtures admixed with PG and CG showed higher compressive strength and combined water contents values than the OPC control at all ages of hydration.
iii) SEM micrographs showed a gelatinous layer composed mainly of gel-like calcium silicate hydrates and calcium hydroxide which covers the unhydrated cement grains, sand particles and fills the micro pores leads to a more compact structure compared to the control mix indicating to higher acceleration in the degree of hydration occurred with PG and CG mixes than that of the OPC mix.
B. OPC admixed with ethylene glycol (EG) and tri ethanol amine (TEA).
i) The Blaine area and grind ability index of OPC mix admixed with EG showed high values than those of control mix and admixed with TEA, while the water of consistency, the initial and final setting times results of dry OPC mix admixed with TEA demonstrated higher values than that of dry OPC mix admixed with EG.
ii) A higher values of compressive strength and combined water contents values were observed with the OPC mixes admixed with EG and TEA than that of OPC control. At later ages of hydration, the OPC mixes admixed with TEA gave higher compressive strength values than those for EG mixes and naturally control mix.
iii) SEM micrographs demonstrated more compact structure of the main hydration products (CSH and CH) as a results of the presence of grinding aids (EG and TEA) admixed with mixes than that of OPC control mix which indicates that the formation of the hydration products was continued to produce a massive structure of improved compressive strength.
C. OPC admixed with a mixtures of propylene glycol (PG) and ethylene glycol (EG) with a ratio of (1:1) by volume, named (PEG).
i) The Blaine arae and grind ability index of OPC mix admixed with PEG at 0.04 and 0.05 wt. % doses showed lower values than those of OPC mix admixed with PG or EG, consequently. The water of consistency and the initial setting times results of OPC mix admixed with PEG demonstrated lower values than that of OPC admixed with PG or EG, while a little rise of final setting times values for PEG admixed with OPC more than PG and EG especially at 0.04 wt. was noted. %.
ii) On comparing the results of compressive strength of the mixes of OPC in presence of PEG mixture as grinding aid with the mixes with PG or EG, there is no great difference.
iii) A moderate and high values of combined water contents for PEG admixed with the control mix were observed at early ages of hydration at both doses of 0.04 and 0.05 wt. % if they compared to EG and PG. Moreover, a higher values of combined water for PEG mixes than those of PG and EG mixes at later ages of hydration for both doses 0.04 and 0.05 wt. %.
D. Portland limestone cement (PLC) admixed with propylene glycol (PG) and commercial grinding aids (CG).
i) Higher values of Blaine and grindability index were observed for OPC-L5 and OPC-L10 mixes admixed with PG and CG than that of OPC-L5 and L10 control at doses, 0.03 and 0.04 wt. %. A remarkable increase of water of consistency values with dose 0.03 wt. represented with PG1L5 and PG1L10 mixtures more than CG1L5 and CG1L10 mixtures was observed, while lower values of water of consistency were noticed at dose 0.04 wt. % for 5 and 10 % LS addition. The initial and setting times values of PG1L5, PG2L5,CG1L5 and CG2L5 mixtures were observed to be higher than OPC-L5 control, while have lower values than OPC-L10 control.
ii) At dose 0.03 wt. %, the compressive strength results demonstrate higher values of PG admixed with OPC-L5 and OPC-L10 control than those of CG admixed with the same control mixes, while appeared lower values at dose 0.04 wt. % at all hydration ages. The combined water results of PG mixes with OPC-L5 and OPC-L10 showed higher values than those of CG mixes at both doses 0.03 and 0.04 wt. %.
iii) SEM micrographs for mix PG2L5 and CG2L5 after 2 days show a more dense structure compared to control mix OPC-L5. After 90 days, SEM micrographs for PG2L5 and CG2L5 show more complete covering of limestone and sand particles with gelatinous layer of the hydration products than that of the control mix OPC-L5.