STUDIES ON THE PROPERTIES OF SOME BLENDED CEMENTS MADE WITH LOCAL MINERAL ADMIXTURE UNDER SULPHATE ATTACK

CONCLUSIONS

The resistance of sulfate attack of cementing materials can be taken by using replacement material suitable for this process. Metakaolin can be safely added to Portland cement to resist sulfate attack. On the other hand, sandy clay can resist attack successfully but with side effect on the physical properties of cement. Limestone as replacement material cannot be used to resist sulfate attack. Finally, 20% metakaolin replacement for 42.5 I cement can be used as mineral admixture for preparing blended cements used as resisting sulphate attack cements.

STUDIES ON THE PROPERTIES OF SOME BLENDED CEMENTS MADE WITH LOCAL MINERAL ADMIXTURE UNDER SULPHATE ATTACK

Rizk, M. ¹ ;  Y. A. Osman¹ ; H.Abbas² and A. Hassan³  

1-Faculty of Science, Helwan University

2-Housing and building research institute

3-  Arabian Cement Company

ABSTRACT:

Three types of replacement materials were used in manufacturing of some blended cements. The characterization, durability and resistance of these prepared blended cements against sulfate aggressive media were studied. The replacement materials used in this study are metakaolin, sandy clay and limestone. Blended cement mortars were prepared with 15, 20, and 25% mineral admixtures replacement instead of the same percent of cement. The specimens were immersed in 5% magnesium sulfate and 5% ammonium sulfate solutions then compared with the samples dipped in distilled water as reference samples for 90 days curing. The compressive strength and expansion of cement mortars were investigated at different time intervals.

The result revealed that metakaolin can be used for resisting sulfate attack without any disadvantages in physical properties of cement. Sandy clay show good results against sulfate attack but causes side effect on physical properties of cement due to its high insoluble residue. However, limestone as mineral admixture not failed to resist o sulfate attack.

1. INTRODUCTION:

The degradation of cementitious materials by external sulfate attack is one of the most frequently cited causes of service life reduction of concrete structures. The importance of sulfate attack is attested by the multitude of experimental and theoretical studies on its origin and manifestations that have been published just in the last decade [1–6]. The formation of ettringite [7–9] and sometimes gypsum [10] are usually thought to be responsible for significant volumetric expansion and structural damage during sulfate attack.

The present work studied the effect of some replacement material on resistance of sulfate attack and its effect on physical properties of cement   

2. EXPERIMENTAL

Blended Portland cements were prepared by mixing CEM I 42.5 N with 15, 20, and 25% of metakaolin, sandy clay and limestone as replacement materials.

The effect of these replacement materials on the water of consistency and setting times of the cement was carried out according to EN196-3:2016(11).

The cement was mixed with sand for preparing mortar samples with the ratio of 1:2, respectively with w/c ratio of 0.46. The Mixing process was performed in compliance to ASTM C 305-20(12). The mortar pastes were molded in 1x1x11.25 inches cm stainless steel molds with test method ASTM C 157 (13) and ASTM C 490 (14), stored 24 h in humidity chamber, demolded then cured in 5% MgSO₄, 5% (NH₄)₂ SO₄ solutions as well as distilled water as reference up to 3 months .The effect of the additives was performed by adding 15, 20, and 25% by weight replacement material to Portland cement then proceeding as described.

The compressive strength of the hardened mortar samples were measured up to 90 days curing according to B.S. EN 196-1:2016(15).

3. RESULTS:

3.1 Characterization of cements

Table 1 illustrates the oxide percentages of CEM I 42.5 N, metakaolin cements (K), sandy clay cement(S) and limestone cement (L).

Table (1):  Oxide composition of CEM I 42.5N (m. %)

Samples legend: OPC (Ordinary Portland cement), L (limestone cements, L1, L2 & L3 are 15, 20 & 25% limestone replacement, respectively) . S (Calcined sandy clay cements S1, S2 &S3 are 15, 20 &, 25% replacement, respectively). K (Calcined kaolin clay cements K1, K2 & K3 are 15, 20 &25% replacement, respectively).

3.2 Water of consistency and setting time

Table2 exhibits the effect of replacement materials on the water of consistency and setting time of Portland cement. The results indicate a clear increase in the water of consistency due to the increase in surface area of cements with the increase of replacement materials. There is a retardation of the cements set with the increase of the replacement material percentage due to the increase of aluminate phases especially kaolin blended cements materials. 

Table (2): Effect of replacement materials on water of consistency and setting time of Portland cement and blended cement pastes

3.3 Expansion

The expansion results of OPC and blended cements immersed in (a) 5%MgSO₄ (b) 5 % ( NH4)₂SO₄ solution (C) distillated water are showed in figure 1. The results indicate that expansion of meta kaolin cements (K1,K2,K3) as well as calcined sandy clay cements (S1,S2,S3)  decreased while increases with limestone cements (L1,L2,L3)  specially with 30% replacement for 90 days curing. Ammonium sulfate salt is more harmful than magnesium sulfate solution.

Figure 1 (a) Expansion of cements  immersed in5%MgSO₄

Figure 1 (b) Expansion of cements  immersed in5 %( NH4)₂SO₄ solution.

Figure 1 (c) Expansion of cements  immersed in distillated water

3.4 Compressive Strength

  The compressive strength of blended cements cured in distillated water, 5%MgSO₄ and 5 %( NH4)₂SO₄ solutions for 2, 7, 28, 90 days are shown in figure 2 (a, b &c). There is a clear reduction in compressive strength of k3 sample (30%) kaolin. This is may be due to the reduction of CSH phase. However, the results of K1 and K2 are agree with the specification B.S. EN 196-1:2016(15). Also reduction of compressive strength with increasing limestone content is due to reduction of the amount of hydraulic phases especially CSH phase.However, compressive strength with calcined sandy clay decreases because of high insoluble residue. 20% kaolin replacement shows the maximum value of compressive strength due to formation of additional hydrated phases resulted from pozzolanic reaction of kaolin.

Figure 2 (a) Compressive strength of cements  immersed in 5%MgSO₄

Figure 2 (b) Compressive strength of cements immersed in 5%(NH₄)₂SO₄ solution

Figure 2 (c) Compressive strength of cements  immersed in distilled wate

X ray diffraction

The X-ray diffraction patterns of Portland cement mortars mixed with 15% metakaolin cured in distilled water,5% magnesium sulfate solution and 5% ammonium sulfate solution  for 3 months are represented in figure 3 (a,b&c), respectively. The figures show that the presence of Ca(OH)₂ , quartz  and traces of gypsum in samples treated with sulphate solutions.

Figure 3 (a) Portland cement mortars mixed with 15% metakaolin cured in distilled water for 3 months

Figure 3 (b) Portland cement mortars mixed with 15% metakaolin cured in 5% magnesium sulfate solution for 3 months

Figure 3 (c) Portland cement mortars mixed with 15% metakaolin cured in 5% ammonium sulfate solution for 3 months

4. DISCUSSION:

4.1 The delayed ettringite formation (DEF)

The delayed ettringite formation has a harmful effect on the hydrated cement systems, depending on its large volume. This large phase causes cracking and damage of hydrated cements or collapsing of concretes. Sulfate attack may internal or external from outside as sea water or sewage and ground water. The process takes place in the core of the cement or concrete causing expansion. This phase appears after 6 months curing, so this phase does not appear in x ray diffraction analysis.

4.2 Resistance of the sulfate attack.

The use of limestone as mineral admixture does not improve sulfate attack resistance because of excess amount of CaO and consequently free lime. On the other hand, metakaolin and sandy clay can resist sulfate attack due to its ability to form additional CSH phases during the hydration process. These precipitated phases decrease the porosity through filling up the space. Hence minimize the ettringite phase formation which need large space to be settled.

5. CONCLUSIONS

The resistance of sulfate attack of cementing materials can be taken by using replacement material suitable for this process. Metakaolin can be safely added to Portland cement to resist sulfate attack. On the other hand, sandy clay can resist attack successfully but with side effect on the physical properties of cement. Limestone as replacement material cannot be used to resist sulfate attack. Finally, 20% metakaolin replacement for 42.5 I cement can be used as mineral admixture for preparing blended cements used as resisting sulphate attack cements.

REFERENCE:

1. Santhanam, M. ; M.D. Cohen and J. Olek (2003): Effects of gypsum formation on the performance of cement mortars during external sulfate attack. Cem. Concr. Res.; 33: 325–332. 

2. Irassar, E.F. ; V.L. Bonavetti and M. González (2003): Microstructural study of sulfate attack on ordinary and limestone portland cements at ambient temperature. Cem. Concr. Res.; 33:31–41. 

3. Tixier, R. and B. Mobasher (2003): Modeling of damage in cement-based materials subjected to external sulfate attack. I: Formulation. J. Mater. Civ. Eng.;15(4):305–313. 

4. Schmidt, T. ; B. Lothenbach ; M. Romer ; J. Neuenschwander and K.L. Scrivener (2009):Physical and microstructural aspects of sulfate attack on ordinary and limestone blended Portland cements. Cem. Concr. Res.;39: 1111–1121. 

5. Sarkar, S.L. ; S. Mahadevan ; J.C.L. Meeussen ; H. van der Sloot and D.S. Kosson (2010): Numerical simulation of cementitious materials degradation under external sulfate attack. Cem. Concr. Composites.,  32: 241–252. 

6. Oliveira, I. ; S.H.P. Cavalaro and A. Aguado (2013):New kinetic model to quantify internal sulfate attack in concrete. Cem. Concr. Res. 2013;43:95–104. 

7. Brown, P.W. and H.F.W. Taylor (1999): The role of ettringite in external sulfate attack. In: Marchand J, Skalny JP, editors. Materials Science of Concrete: Sulfate Attack Mechanisms. American Ceramic Society; Westerville, OH:. pp. 73–98. 

8. Clifton, J.R. and J.M. Pommersheim (1994):Sulfate attack of cementitious materials: Volumetric relations and expansions, NIST Interagency Report 5390. National Institute of Standards and Technology; Gaithersburg, MD: Apr, 1994. [July 23, 2015]. Available at http://fire.nist.gov/bfrlpubs/build94/PDF/b94040.pdf. [Google Scholar]

9. Gollop, R.S. and H.F.W. Taylor (1992): Microstructural and microanalytical studies of sulfate attack I. ordinary portland cement paste. Cem. Concr. Res.;22:1027–1038

10. Tian, B. and M.D. Cohen (2000): Does gypsum formation during sulfate attack on concrete lead to expansion? Cem. Concr. Res.;30:117–123. 

11.EN196-3(2016). Method of testing cement-part3: determination of setting times and soundness.

12. ASTM C305-20. Standard practice for mechanical mixing of hydraulic cement pastes and mortars of plastic consistency

13. ASTM C 157/C157M-17:(2017):  Standard test method for length change of hardened hydraulic-cement mortar and concrete.

14. ASTM C 490/C490M-17:(2017): Standard test method for use of apparatus for the determination of length change of hardened cement past, mortar, and concrete.

15. 135EN196-1:2016. Methods of testing cement. determination of strength

دراسات على خواص بعض الاسمنتات المخلوطة المصنعة من اضافات معدنية محلية ومعالجة فياوساط کبريتية

محمد رزق¹، ياسر عبد التواب عثمان ¹، حسن عباس ² ، علي حسن ³ 

  1  - کلیة العلوم، جامعة حلوان 2- مرکز بحوث الاسکان و البناء  3- الشرکة العربية الاسمنت

تتعرض بعض  المباني لمهاجمة تفاعل املاح الکبريتات خاصة الموجودة في المناطق الساحلية او بجوار الصرف الصحي هذا التفاعل ينشأ عنه ملح الاترنجيت الذي يسبب تمدد وهدم في الخرسانة مع مرور الوقت لذلک  فعلنا دراسة لايجاد طريقة  لمقاومة مهاجمة هذه الاملاح .

تم خلط الاسمنت البورتلاندي العادي بمواد بديلة للاسمنت  مثل الحجرالجيري و طفلة ميتاکاولينا وطفلة رمليه محروقة بنسب   15, 20 و25% وتم معالجتهم في املاح الکبريتات مثل املاح کبريتات الماغنسيوم واملاح 15, 20 و25% کبيرتات الامونيوم لمدة ثلاثة اشهر.

 تم دراسة تأثير هذه الاملاح على الخصائص الفزيائية  للاسمنتات المخلوطة بالمواد البديلة مثل التمدد وقوه تحمل الضغط ومقارنتها ايضا بالمعالجة في الماء.

واظهرت  ان الاسمنت المخلوط بالميتاکاولينا کان جيد حيث انه حتى  لم يتعدى المواصفات القياسية وکان مقاوم جيد لاملاح الکبريتات ونتائج قوة تحمل الضغط اثبتت انه في حالة خلط  الاسمنت بنسبة 15, 20 و25% مع الميتا کاولينا لا تتجاوز المواصفات القياسية ولکن الخلط بنسبة 25% تتجاوزت الحد المسبوح به

وايضا وجد ان  الاسمنت المخلوط بالطفلة الرملية المحروقة مقاوم جيد  لاملاح الکبريتات لان نتائج التمدد کانت جيدة ولکن قوة تحمل الضغط  کانت ضعيفة بسبب انها تحتوي على نسبة عالية من المواد الغير ذائبة .

بينما الاسمنت المخلوط بالحجر الجيري وجد انه لا يکون مقاوم جيد لاملاح الکبيرتات لانه حقق نتائج عالية في التمدد وقوة التحمل الضغط کانت ضعيفة .