Study The Contribution In The Additions Mineral On The Paste, Mortar And Their Impact On Total Porsity

By
Guimer Tarek and Mellas Mekki
Department of Civil Engineering, Mohamed Khider University, Biskra, BP 145, Biskra 07000, Algeria
Tel fax: 033 73 45 28

Abstract
This work aims to study the evolution of the resistance of Portland cement pastes and mortars containing two mineral additions such as calcareous filler and finely crushed slag.

The effects of the addition of two mineral additions to Portland cement pastes are mortars, has been carried to evaluate the evolution of the mechanical resistance as function of the age and the mode of the treatment .This study is a simplified approach to show the contribution of the mineral addition on the development of the mechanical resistance, and the porosity obtained using methanol exchange method. In addition, to confirm this study and based on laboratory test resorts approximate equations were obtained

Keywords: Porosities, cement paste, mortar, mechanical resistance, exchange by methanol.

INTRODUCTION
It is widely recognized that the porosity of a material exerts an enormous influences on its physical proprieties. For hardened cement paste a large volume of pores is inherent in the set structure. This porosity is derived mainly from excess water required to ensure cement hydration and provide workability of cement paste, but can also be present due to inadequate compaction. The residue of water filled space in fresh cement paste becomes voids in hardened cement paste. These voids are divided in two classes, capillary pores and gel pores .the former represent the volume of the capillary pores and it depends mainly on both water/ cement ratio of the mix and the degree of hydration. The latter represents the gel pores. As hydration progresses, the amount and distribution of porosity between capillary and gel pores will change. Initially all the pores are capillary pores. As hydration precedes the capillary pore volume is reduced because the capillary space becomes filled with hydration products, and the gel porosity increases. There is a net reduction in total porosity.

During the last fifteen years Mercury intrusion proximity which involve forcing mercury into pores of a body by application of pressure and assuming that all pores have a simple shape, Has been used for determining the pore structures sizes of hydrated cement paste. This method enables a wide range of pore-size distribution to be measured between 1000µm and 30A° depending on the pressure [Orr; 1970]. However, the application of great pressure on hydrated cement paste may cause destruction in the structure and pores below 30A cannot be considered [Shi D and Winslow D N 1985] . In addition to this method there are other investigation involving fluid replacement as methanol and helium pycnometry. The use of methanol as displacement medium for porosity measurement [Scrivener, K L and P l ,1984], have indicated that the porosity values were equivalent to those when helium was used as displacement method. [Parrot, 1981] reported on the effect of drying upon the exchange of pore water with methanol. He found that the water/methanol exchange results of 0.6 water/cement ratio by weight pastes indicated that the pore volume penetration by methanol was only on average 0.7 per cent greater than that occupied by original pore water and the exchange provided reliable pore structure information.

The objective of the current study is to empirically evaluate the participation of physicochemical, microstructures and possibly chemical of the mineral additions on the physical and the mechanical proprieties and the durability of the cement pastes and mortars while being freed from their granular effect. For that a specific experiment al methodology was developed based on the estimation of the impact of the mineral addition built-in in the mixture and to examine their reactivity starting from type of introduced addition and then to measure the total porosity of the mixture (paste / mortar) using methanol to appreciate it. Two mineral addition of different characteristic were introduced to estimate resistance in compression.

Materials
The used cement is a composed Portland cement, produced by cement plant located at AIN-TOUTA , kinds of cement powders were used with Blaine fineness of about 3371 cm²/g (CPJ). The physical properties and chemical analysis of the cement and are listed in Table 1.

The slag powders were used with Blaine fineness of about 3500 cm²/g (Slag S) and 4080 cm²/g (Filler F). The physical properties and chemical analysis of the slag powders and calcareous filler and are listed in Table 2 and 3, respectively.

Table 1: chemical composition of cement

Chemical Composition (%)								Mineralogical Composition (%)
SiO2	Al2O	Fe2O	CaO	MgO	Free lime	Residue insoluble	Loss on the ignition	C3S	C2S	C3A	C4AF
22,00	5,30	3,38	65,16	1,77	2,32	1,40	0,48	58,09	23,32	8,32	10,27

Table 2: Chemical composition of slag.

Components	SiO2	Al2 O3	FeO	CaO	MgO	MnO	S
(%)	40,80	5,2	0,53	43,01	6,4	3,02	0,8

Table3 Chemical compositions of the calcareous fillers.

SiO2	Fe2O3	Al2O3	CaO	MgO	SO3	NaCl	LOSS ON FIRE
0.58	0.02	0.06	55.80	0.06	0.08	0.56	43.53

THE EXPERIMENTAL PLAN
The study was based on the use of a Portland cement made up with the mineral additions of matters such as: the slag (S) and calcareous filler (F) matter separately and with various percentages. The goal considered is on the one hand the evaluation of the rate of participation of these additions and their influence on the mechanical resistance according to time, and of another share the test makes it possible to evaluate existing total porosity in each of the two elements.

1) For the cement paste one used a Portland cement made up (CPJ) of resistance characteristic (42.5 Mpa) for a weight of (20±2) g and a variable (w/c ) ratios between (0.3÷0.6) with the various mineral additions previously quoted.

2) With regard to the mortar, one used the sand of wade with a constant rate of (1350±2) g by preserving same report W/C ratios quoted previously with the change of the quantity of water following the change of report/ratio (w/c)

INVESTIGATION METHODS
The porosity was measured by using the methanol exchange method (MEM).

Methanol exchange:
Determination of the porosity has been achieved by method of solvent replacement. Analar grade methanol was used which can penetrate into the micro-structure without damage. The unbound water in the specimen was replaced by methanol, thus the hydration was arrested and all water eventually replaced by methanol; this is shown by a constant weight of the specimen between 3 and 14days, Specimens were then dried over silica gel for 24 hours at 20 °C. The porosity was measured using methanol exchange [Parrott .1981].

Specimen preparation:
Several small prisms (40*40*160 mm) and cubes 20 mm sides) were cast with water/cement ratios by weight ranged between 0.30and 0.6. Mixing was prolonged and intermitted to minimize bleeding. Careful curing ensured wet conditions for surfaces for the first 24 hours. Following demoulding, samples were kept under wet and dry curing conditions and chosen for test at ages which provided has variation in the porosity. When selected for analysis, cubes were tested in compression. Prisms were cut perpendicular to the longitudinal axis with a diamond saw to yield has 3 mm thick slice. Samples were then immersed immediately in methanol to prevent carbonation and stop hydration prior to the determination of porosity.
Summary of necessary time to produce a sample of hydrated cement paste and mortars are given below, where the limit between brackets time is undertaken for each operation.

• Cutting the sample to yield 3 mm thick slices, (15 mn).
• Drying the sample by methanol exchange, (15 days).
• The samples dryness it stored on silica gel, (15days)

Detail of methanol exchange Method:
The volume of the pores was obtained starting from the weight of the sample saturated superficially dry by methanol minus the dry weight, after having to store the sample in silica gel, divided by the density of methanol.

Vm = (Mss-Ma)/ym
Where
Vm – volume of methanol (cm³)
Mss – mass saturated superficially dry (g)
Ma -The mass dryness (g)
ym – density of methanol (G/cm³)
Pm = Vm/Vt
Pm – porosity by methanol exchange (%)
Vt – total volume (Vt=Vs+Vp)
Vs- the solid volume of a material (cm³)
Vp – the volume of the pores (cm³)

EXPERIMENTAL RESULTS AND DISCUSSION
Cement paste: The effect of (w/c) ratio on the porosities of cement paste is shown in Table4. The porosity of hydrated cement based upon methanol exchange as a function of various water cement ratio of different additive content with ages is shown in Fig1.

The mortar, The effect between (w/c) ratios and the porosities of mortars is shown in Table5. The porosity of hydrated mortars cements upon methanol exchange as a function of various water cement ratio of different additive content with ages is shown in Fig2.

Table4 Results of The porosity obtained by MEM and W/C ratio for cement paste without additions.

W/C	0,3	0,35	0,4	0,45	0,5	0,55	0,6
CPJ	3,04345	3,20655	3,29655	3,31655	3,74095	4,10139	4,19640
10%F	0,78957	0,87231	0,96717	1,22612	2,10345	3,39715	3,73607
15%S	0,78942	1,19732	1,35939	1,82054	3,14370	3,29588	4,24402

Table5: Relation between porosity and the W/C ratio for mortar without addition

W/C	0.3	0.35	0.4	0.45	0.5	0.55	0.6
CPJ	11,7823	12,04564	14,27554	14 ,20532	16,37753	17,01234	25,15748
10%F	8,31419	8,45825	9,94493	11,33915	12,13005	17,25100	18,35494
15%S	10,69125	10,71575	11,28004	13,74814	14,04163	15,35882	17,22200

Based on methanol exchange porosity test results, it can be noticed that.
Firstly: For the cement paste, the porosity with 10% of filler is lower than that with 15% of slag, and by comparing the results obtained we notices that there is an increase in porosity for the cement paste without additions. That clearly shows us the role of the mineral additions in the reduction of porosity.

Secondly: For the mortar, we notices the same preceding results, but with a small change. For porosity of with (w/c ) ratio equals for 0,6 for mortar containing 10% F, and that containing 15% S, porosity decreased for the mortar with 15% S because the existence of a significant portion of silica as constituting matter added (the slag) in addition to the existence of the sand which contains in its turn the same component (silica).

One can conclude the following points:
• Porosity depends on (w/c ) ratio.

• The reduction of porosity depends on the rate of fineness of the added mineral matter and the rate of its pozzolanic effectiveness to limit this phenomenon.

• The mechanical resistance depends on the reduction of porosity.

• The mineral additions do not contribute to form a significant volume of new hydrated products able to reduce the porosity of the mortars even if resistance in compression can be more or less improved by the flexible activity of the additions in the presence of cement.The flexible contribution of the mineral additions thus has structuring role of the connections of the cementing matrix from the mechanical point of view that a role quantitative role on the reduction of porosity [Anissa Bessa and others.2004].

• This study confirms the effect of (w/c) ratio of cement paste and mortar on the porosity obtained by methanol exchange method.

Without forgetting the studies, realized by [Parrott,1981], which confirms only any risk of modification on the level of the microstructure, of the paste of cement and the mortar.

RELATION BETWEEN MECHANICAL RESISTANCE AND W/C RATIO
The effect of W/C ratio on the mechanical resistance (compressive strength) of mortar is shown in Figure3,4 and 5, respectively.

According to test results, it can be noticed that the mechanical resistance is affected by the water/cement ratio as the mechanical resistance decreases with the increase of water/cement ratio and appreciably the porosity decreases. The increase in cement proportioning and the choice of its type have a favorable influence on the reduction in porosity; the hydrates formed by the hydration of cement have an essential role of filling of the capillaries, and consequently increases the mechanical resistance.

The contribution of the siliceous additions and of the same limestone’s fineness is completely comparable, as well as the absence of a significant chemical effect. Let us note that the fineness supports the physicochemical effect of the additions. Indeed, the presence of a great number of submicron particles in the cementing matrix around the cement grains multiplies the possibilities of germination of the hydrated products and develops micro-structural complexity and the effectiveness of the connections [Anissa Bessa and others.2004].

CONCLUSIONS:
Based on the results of this experimental investigation, the following conclusion can be obtained:
1. The use of mineral additions such as fine slag and calcareous fillers reduces the porosity of cement paste and mortar.
2. Methanol exchange method is a reliable testing method which can be used to obtain the porosity of cement paste and mortar.
3. The increase of water/cement ratio increases the porosity and decreases the compressive strength of cement paste and mortar.

ACKNOWLEDGMENTS
The authors wish to express their gratitude and sincere appreciation to the authority of Port and Airport Research Institute, civil engineering for financing this research work and also several on-going research projects related to Contribution to the mineral addition on the characteristics physiquo-mechanics of the paste of cement and mortar.

REFERENCES
1. Anissa, B., Jean-Philippe. B., and Jean-Louis ,G. ,.” Evaluation of the flexible contribution of additions minerals a porosity, a compressive strength and the durability of the mortars” 22 “èmes university meetings of Civil Engineering, Price Rene Huppert. 2004.
2. Mezghiche, B., A, Boudchicha.” Use of a new approach méthodologique for the evaluation of the effect of additions minerals on the proprieties of the cementing mélanges.
Colloque CMEDIMAT, 06- 07 December, 2005.
3. Lawrence .,P., “on the activity of the fly-ashes and the chemically inert mineral additions in cementing materials “, Thesis of doctorate., INSA of Toulouse ,2000.
4.Parrott, L., J. 1981. “Effect of drying history upon the exchange of pore water with methanol and upon subsequent methanol sorption behavior in hydrated alit paste “ Cement and Concrete Research, Vol .11,p 651 – 658.

We at engineeringcivil.com are grateful to Er.Guimer Tarek for submitting this very useful paper to us. Hope this will help many civil engineers around the world in understanding the impact of adding additional materials on porosity of mortar.

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