INNOVATIVE COMPOSITE MATERIALS FOR STRENGTHENING LIME - BASED MORTARS IN TRADITIONAL MASONRY STRUCTURES Текст научной статьи по специальности «Химические науки»

УДК 666.971

DOI: https://doi.org/10.31659/0585-430X-2019-773-8-42-47

М. АБДУЛМАДЖИД1, д-р, преподаватель, кафедра реставрации, археологический факультет ([email protected]),

М. КАССАБ1, д-р, преподаватель, кафедра инженерной физики, инженерный факультет; Х. ШУКРИ2, исследователь; С. ТАХА1, проф., кафедра физики, научный факультет

1 Университет Фаюм, Египет (http://www.fayoum.edu.eg/english/)

2 Национальный исследовательский центр жилищного строительства, Египет (http://www.hbrc.edu.eg/)

Инновационные композитные материалы для укрепления известковых растворов в традиционных каменных конструкциях

Потребность в новом инновационном известковом растворе, пригодном для реставрации и ремонта исторических зданий, в последнее время стала предметом многих исследований. Новый раствор должен, однако, удовлетворять следующим требованиям: иметь те же физические и механические свойства, что и у существующего старого раствора; распределение по размерам пор должно быть сопоставимо с распределением старого известково-песчаного раствора; раствор должен быстро схватываться как в сухой, так и во влажной среде. Основная цель представленного исследования - разработка инновационного строительного раствора на основе извести, который был бы пригоден для реставрации древних сооружений. Для достижения этой цели были подготовлены две группы растворов различного состава на основе извести, обозначенных как S1 и S2. Каждая группа состояла из четырех разных смесей. В составы группы S1 входили песок, известь, гипс, цемент, хомра*. В группе S2 были составы, идентичные составам в S1, но с добавлением постоянного количества пуццолановой добавки (зола уноса). Каждая композиция может быть определена с точки зрения ее составляющих как (г1 :г2:г3:г4:г5:г6), где эти г означают объемное соотношение каждого компонента материала (песок: известь: гипс: цемент: «хомра»: зола уноса). Для этих восьми растворов были проведены испытания по определению прочности при сжатии. Кроме этого исследовались такие физические свойства, как насыпная плотность, коэффициент пористости и коэффициент водопоглощения. По результатам испытаний установлено, что физические свойства всех составов удовлетворительные. Отмечено, что раствор В0 (3:2:2:0:0:0) из группы S1, в состав которой не вводили золу уноса, имеет лучшие из всех физические характеристики и высокую прочность. Это связано со скоростью образования гидратной извести, кинетики карбонизации и скоростью механизма схватывания гипса. Было обнаружено, что для композиций растворов из группы S2 с золой уноса в качестве активной минеральной добавки, раствор D (3:1:1:0:0,25:0,5) показал наилучшие физико-механические характеристики. Это связано с высокой поверхностной энергией золы уноса и большим содержанием силикатных частиц и оксидов алюминия как в золе уноса, так и в «хомре». Эти два эффекта приводят к высокой потенциальной реакции гидратации в системе D. Таким образом, можно сделать вывод, что разработанный раствор D является хорошим и по существу инновационным строительным материалом, который можно использовать в качестве восстановительного строительного раствора при ремонте старых зданий и сооружений.

Ключевые слова: реставрация, пуццолановые материалы, известь, строительный раствор, пористость, прочность при сжатии, гидратация, зола уноса.

* «Хомра» — арабская терминология, обозначает пыль красного кирпича (кирпичная пыль). Прим. редактора.

Для цитирования: Абдулмаджид М., Кассаб М., Шукри Х., Таха С. Инновационные композитные материалы для укрепления известковых растворов в традиционных каменных конструкциях // Строительные материалы. 2019. № 8. С. 42-47. 001: 11^:// doi.org/10.31659/0585-430X-2019-773-8-42-47

M. ABDELMEGEED1, Dr., Lecturer, Restoration Department, Faculty of Archaeology ([email protected]) M. KASSAB1, Dr., Lecturer, Department of Engineering Physics, Faculty of Engineering; H. SHOUKRY2, Researcher; S. TAHA1, Prof., Department of Physics, Faculty of Science

1 Fayoum University, Egypt (http://www.fayoum.edu.eg/english/)

2 Housing &Building National Research Center, Egypt (http://www.hbrc.edu.eg/)

Innovative Composite Materials for Strengthening Lime-based Mortars in Traditional Masonry Structures

The need for new innovative lime-based mortar suitable for restoring and repairing historical buildings has recently become the subject of many research studies. The new mortar should, however, fulfill the following requirements: (a) to have the same physical and mechanical properties as that of the pre-existent old mortar; (b) the pore-size distribution is comparable with that of old lime-sand mortar, and finally; (c) the mortar should set rapidly in both dry and moist environment. The main goal of our study is to find an innovative lime-based mortar which is good enough to be used in the field of restoration of the ancient structures. In order to achieve this goal, two different sets of lime-based mortars tagged as S1 and S2, have been prepared. Each set consists of four different mixtures. The test or the reference set S1, consists of four different (sand : lime : gypsum : white cement : homra*) mortar compositions. If a constant amount of pozzolanic material such as fly ash (FA) is add to each mortar composition in set S1 we then get the other set S2. Each composition can be defined in terms of its constituents as (r1:r2:r3:r4:r5:r6), where these r's stand for the volume ratio of each component material (sand: lime: gypsum: cement: homra: FA). These eight mortars were tested for the compressive strength. Moreover, the physical properties such as the bulk density, the porosity ratio, and the water absorption ratio were obtained for each mortar. The obtained results for the physical properties of these mortar compositions revealed that the mortar B0 (3:2:2:0:0:0), i.e. without fly ash, has good physi-

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cal characteristics and high strengths as well. This is related to the rate of hydrate lime, carbonation kinetic, and the speed of setting mechanism for gypsum. For those mortar compositions with fly ash as an additive, it was found the mortar composition D (3:1:1:0:0.25:0.5) has very good physical and mechanical characteristics. This is attributed to the high surface energy of the fly ash, and to the large content of silicate and aluminum oxides in both the fly ash and homra. These two effects lead to a high potential hydration reaction in the D system. Thus, it can be concluded that, the mortar system D is a good and a substantially innovative mortar which can be utilized as a restoration mortar in repairing old buildings and structures.

Keywords: restoration, pozzolanic materials, lime, mortar, porosity, compressive strength, hydration, fly ash.

* Homra — it is an Arabic terminology and the English translation is the dust of red brick (Brick Dust Waste (BDW).

For citation: Abdelmegeed M., Kassab M., Shoukry H., Taha S. Innovative composite materials for strengthening lime-based mortars in traditional masonry structures. Stroitel'nye Materialy [Construction Materials]. 2019. No. 8, pp. 42-47. (In English). DOI: https://doi.org/10.31659/0585-430X-2019-773-8-42-47

Introduction

A general requirement for materials to be used in the repair of ancient structures is that, they should not cause an acceleration of the deterioration rate of adjoining ancient material. This holds not only for buildings but in general for objects of any type. Since most ancient masonry in Egypt is made of lime-sand mortars, it is favorable to use of traditional lime mortar for masonry repair. However, water addition to lime mortar, improves workability but tends to reduce mechanical strength. Moreover, lime-based mortars are slow-setting and require a relatively dry environment. In moist ancient structures, lime may set very poorly or not at all. Setting of lime depends upon carbon dioxide from the air reacting with the mortar. In thick structures, carbonation of the core is extremely slow and unreliable. From the mechanical point of view, the properties of well-set lime mortars are quite adequate. Furthermore, they present some specific characteristics that may be regarded as desirable. The need for new innovative lime-based mortar suitable for restoring and repairing historical buildings has recently become the subject of many research works. The new mortar should, however, fulfill the following requirements; a — it has the same physical and mechanical properties as that of the pre-existent old mortar; b — the pore-size distribution is comparable with that of old lime-sand mortar, and finally; c — the mortar should set rapidly in both dry and moist environment [1].

The addition of some pozzolanic material such as fly ash (FA), nano-kaolin (NK), and silica fume (SF), to the original old restoring mortars, is considered a new trend to

Table 1 Таблица 1

New lime-based mortar compositions on volumetric ratio basis

Новые известковые составы растворов на основе объемного соотношения

Material / Материал S1 S2

Ac Bo Co Do A B C D

Sand / Песок 3 3 3 3 3 3 3 3

Lime / Известь 1 2 1 1 1 2 1 1

Gypsum / Гипс 1 2 1 1 1 2 1 1

White Cement / Белый цемент - - 1 - - - 1 -

Homra / Хомра - - - 1/4 - - - 1/4

Fly Ash (FA) / зола уноса - - - - 1/2 1/2 1/2 1/2

improve the physico-mechanical properties of the old mortar materials. Moreover, it enhances the durability, and the workability of the old mortar used in the field of the restoration of the cultural heritage buildings. In the mortar mixture, the added materials take part in the hydration reaction, and also contribute to the formation of a new microstructure of any mortar mixture [2, 3]. The activity of the pozzolanic material with the pre-existent mortar system, leads to a variations in the hydration products. This in turn give changes in the physico-mechanical properties of the mortar, which are dependent on the morphology and the microstructure variations during the hydration process of the new mortar [4, 5].

In this sense, the addition of pozzolanic material to the original mortar will enhance the durability, workability, and the strength of the new mortar (innovative composite material), make it compatible with the pre-existent old mortar and thus becomes useful in the restoration of historical buildings [6].

The main objective of the current study is to develop a new durable, modified lime-based mortar with adequate strength and an enhanced workability for the restoration of the ancient historical structures.

Materials and methods

Experimental. Two different systems tagged as S1 and S2 of lime-based mortar mixtures were prepared following the composition recipe shown in Table 1.

The mortar system S1 is composed of four different mixtures tagged as Aq, B0, C0, and D0. Each sample composition was prepared on volumetric basis. The composition of each sample was grinded together for 30 minutes and then was poured in a mixer machine in order to prepare a mixture with a high degree of homogeneity. After the mixing process the consistency water was added to initiate the hydration process. All the mixtures were then casted in 5 cm3 cubic molds, test mixtures S1 were remolded after 3 days and stored at normal room temperature and pressure.

The mortar system S2 is composed of four different mixtures tagged as A, B, C, and D. Each sample composition was prepared on a volumetric basis. The mixtures were prepared following the same procedures except that an extra constant amount of fly ash (FA) is added for each mixture.

After 3 days as a curing time, the physico-mechanical properties such as the bulk density pb, the water absorption ratio Wa (%), the porosity ratio P(%), and the com-

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Table 2 Таблица 2

The physico-mechanical properties of test system S1 Физико-механические свойства системы S1

System / Состав Physical Properties / Физические свойства Mechanical Properties / Механические свойства

Bulk Density (g/cm3) / Объемная плотность (г/см3) pd Water Absorption / Коэффициент водопоглощения, Wa (%) Porosity / Пористость, P (%) Compressive Strength (Kg/cm2) / Прочность при сжатии (кг/см2)

Ao 2.416 17X10-3 41X10-3 2.8

Bo 3.987 8.7X10-3 35X10-3 13.06

Co 3.241 10X10-3 47X10-3 10.4

Do 1.98 26X10-3 89X10-3 8

pressive strength were performed for all mixtures. Moreover, the microstructure for the test system S1 was performed by the help of SEM techniques [7]. The chemical compositions of different matrices and the additive material (FA) are presented in a previous work [8, 9].

The compressive strength test was carried out by using a german machine with a loading rate of 100 kg/min, and the bulk density pb, the water absorption ratio Wa (%), and the porosity ratio P (%) were obtained according to the equations (1—3):

P4 =

W =

P =

D ws-su' (1) s et H É-¿■8

D ' (2) ш 0 B н

W-D ws-su' (3) .£= -û 1- S а ш

where, Ws is the saturated weight in the air, Su is the suspended weight in water, and D is the dry weight of the sample at about 100oC [7].

Results

The variations of physico-mechanical properties of the different mortar system S1 (Aq , B0, C0, and D0), are tabulated in Table 2 and are shown in Fig. 1 and Fig. 2.

The variation of the compressive strength for the different mixtures of the test system S1 (A0, B0, C0, and D0) are shown in Fig. (1). It is obvious that compressive

ф *

E о

О ,

1.275 1.010 0.785

0.275

Ас B0 C0

Mortar Mixture Растворная смесь

Рис. 1. The variation of the compressive strength Fig. 1. Прочность при сжатии составов S1

Do

strength depends upon the composition of the mixture. It can be also shown that the mortar mixture B0 has the maximum value for the compressive strength as compared with the other mortar mixtures (A0, C0, and D0). This may be attributed to the decrease carbonation kinetics and setting process during the hydration mechanism of the mortar system B0. Fig. 2 illustrates the variation of the bulk density pb, the porosity ratio P (%), and the water absorp-

4

3

2

1

b 0,1

ж ж 0,08

Оч о,-

tio ть 0,06

Ë P

S о сл S 0,04

° д

0,02

0

c

0,03

•É £

с S» 0 ? 0,02

o СЛ g JD E5 a о 0,01

j» о

о > m

0

B0 C0

Mortar Mixture Растворная смесь

B0 C0 Mortar Mixture Растворная смесь

B0 C0 Mortar Mixture Растворная смесь

Рис. 2. Variations of the physico-mechanical properties S1: a - the bulk density; b - the porosity ratio P (%); c - the water absorption ratio, Wa (%) Fig. 2. Физико-механические свойства S1: a - насыпная плотность; b -пористость, P (%); c - водопоглощение, Wa (%)

a

0

научно-технический и производственный журнал ô'J'f;CJi,J'J'5JJiij-liiJ5 "44 август 2019 ЙДГЗЙ!ШЭГ

Table 3 Таблица 3

The physico-mechanical properties of system S2 Физико-механические свойства системы S2

System / Состав Physical Properties / Физические свойства Mechanical Properties / Механические свойства

Bulk Density (g/cm3) / Насыпная плотность (г/см3) pd Water Absorption / Водопоглощение, Wa (%) Porosity / Пористость, P (%) Compressive Strength (Kg/cm2) / Прочность при сжатии (кг/см2)

A 2.8617 39X10-3 98X10-3 4.42

B 2.9314 29X10-3 84X10-3 5.36

C 3.372 17X10-3 69X10-3 8.95

D 4.601 14X10-3 39X10-3 15.6

tion ratio Wa (%), respectively, for the different mortar mixtures (Aq, B0, C0, and D0). It can be shown that the mortar mixture B0, compared with the other mixtures, has the maximum value for bulk density and the minimum value for both the porosity the water absorption ratios. These results, however, supports the result of the compressive strength for the mixture B0. This can be attributed to the higher mechanical strength of gypsum as well as the carbonation kinetic process in the lime base of the mortar which lead to an improvement in the microstructure of the pore-system [10, 11].

After the addition of the fly ash to the test mixtures (Aq, B0, C0, and D0), we get the system S2 of the modified mixtures (A, B, C, and D). The variation of the physical properties with different mixture composition (A, B, C, and D) as well as the compressive strength, were then obtained and tabulated in Table 3, and illustrated in Fig. 3 and Fig. 4.

Fig. 3 illustrates the variation of the compressive strength with the different mixtures A, B, C, and D at early hydration age. The development of compressive strength for each mixture depends on the constituents of each mixtures and the rate of reactivity of the pozzolanic material FA in each system matrix [10]. The pozzolanic material FA has a high reactivity potential for interaction with the free lime at early time of hydration due to its high surface energy of interaction. The fly ash FA is rich with silica and aluminum oxides. All of these factors, lead to the enhanced interaction potential of the fly ash with the

i= w

Ф *

« s

ф d.

E о

О ,

1.520

0.883

0.441 0.490

А B C

Mortar Mixture Растворная смесь

Рис. 3. Variation of the compressive strength

Fig. 3. Прочность при сжатии составов S2

free lime [9]. Fig. 3 shows that the mixture D has the maximum compressive strength compared with the other mixtures. This result is related to the high potential for interaction of the FA with the constituent materials in the mixture D. In the sense that, the mixture contains homra which is also very rich with silica and aluminum oxides, the pozzolanic reaction leads to the formation of hydraulic calcium silicate hydrate, calcium aluminate silicate hydrate gel phases, allowing a higher degree in the setting

4

3

2

1

as ж

0,12 0,1 0,08 0,06 0,04 0,02 0

c

« ~ 0,12

1 ^ 0,1 0,

й <5 0,04

1 I 0,02

0

B C

Mortar Mixture Растворная смесь

B C

Mortar Mixture Растворная смесь

А

D

B C

Mortar Mixture Растворная смесь

Рис. 4. Variations of the physico-mechanical properties S2: a - the bulk density; b - the porosity ratio, P (%); c - the water absorption ratio, Wa (%) Fig. 4. Физико-механические свойства S2: a - насыпная плотность; b - пористость, P (%); c - водопоглощение, Wa (%)

5

a

0

А

D

b

А

D

D

Ц научно-технический и производственный журнал

Л] ® август 2019 45

Рис. 5. The SEM micrograph of repairing material used in the ancient and traditional building Fig. 5. Микрофотография ремонтного материала, используемого в старинном и традиционном строительстве

чж VL иЛ4" i 1ИГЧ tvi г

а

ШЁШ

Рис. 6. The microstructure for the test mortars: a - A0; b - B0; c - C0; d- D0 Fig. 6. Микроструктура исследуемых растворов: a - A0; b - B0; c - C0; d- D0

process and a higher earlier strength to the mortar system [12]. The prediction of the changes in the mechanical properties in any mortar mixture is attributed to the interaction potential that takes place in the mortar during the hydration mechanism. This reaction leads to changes in the transport properties and in the microstructure of the system [4].

Fig. 4 illustrates the variation in the physical properties, the bulk density, the porosity, and the water absorption for the different mixtures A, B, C, D. The higher value of the bulk density for the D system is mainly related to the pozzolanic interaction in the matrix, which is serving as precipitation nucleus for the CSH and CASH gel hydrated phases originating from the hydration process, after the initiation of potential interaction of the pozzolanic inside the system. This makes the system more denser in its structure, i. e., increasing the bulk density. The decreasing of the porosity of the D mixture as shown in Fig. 4, b is related to the higher density of this system, besides the rate of hydration product phases participated in the pore system, leading to a decrease in the pore size and its diameter. Also, it can be shown that in Fig. 4, c the water absorption ratio for the system D is lower than that of the other systems, due to the higher value of the bulk density for system D [13, 14]. All the physico-mechanical properties of the original (Aq, B0, C0, D0) before the addition of fly ash in (A, B, C, D) systems, supported each other.

The microstructures of the original repairing material, which are compatible with the ancient and traditional buildings are mainly dependent on lime-based mortar, which is hydrated to CaCO3. Fig. 5 shows the SEM micrograph for the hydration products of this mortar [15].

The binder of the CaCO3 in the repairing mortars is not enough to reinforce the binder in the ancient building besides the distribution of vacancy space of air inside this mortar.

Fig. 6 shows the microstructure for the test mortars Aq, B0, C0, and D0 which depends on the variation of the physico-mechanical properties. Hence, we can find that B0 matrix system is the best system before the addition of the fly ash [10], and in this respect, system D has the best characteristics after the addition of the fly ash. Thus, it can be concluded that the system D is the required innovative mortar system that satisfy the condition of high workability and durability for the restoration of the ancient buildings.

Conclusions

Based on these results of the physico-mechanical properties for different mortars with and without pozzola-nic activity, the following conclusions can be drawn.

The traditional materials, which were used in repairing process of the ancient buildings in the past, are inadequate for the conservation and repairing process due to the kinetic carbonation of free lime.

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The variation in the physico-mechanical and the microstructure of the B0 system revealed a high durable hydraulic mortar than the other ones. This is due to the high reactive potential of free lime and gypsum in this system.

The activity of the pozzolanic material FA leads to a high activity potential reaction, due to the chemical and mineralogical composition, morphology, fitness and the amount of glass phase, so that the reaction potential of FA in the D system improves the durability, the microstructure and reinforce of the binder repairing material in this system

Due to the high characterizations in the physical properties of the D system, we conclude that FA is a good pozzolanic material at early age of hydration, and system D can be considered as an innovative mortar and can be used as a repairing material for restoration of the ancient buildings.

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г.

Институт строительных материалов им. Ф.А. Фингера (FIB)

Университета Bauhaus-Universität г. Веймар (Германия) организует IV Веймарскую конференцию по гипсу

F1 B Гипс в строительстве, и не только

Веймар (Германия)

1-2 апреля 2020 г.

Основные темы конференции:

■ Вяжущие вещества на основе сульфата кальция

■ Вяжущие вещества, содержащие сульфат кальция

■ Гидратация и переработка

■ Добавки и их эффект

■ Стройматериалы и изделия на основе сульфата кальция

Заявки на участие в конференции с докладами принимаются до 15 октября 2019 г. Планируется синхронный перевод: немецкий, английский, русский.

[email protected]

Сульфаты кальция и сохранение исторического наследия

Изделия на основе сульфата кальция и их безотказное длительное использование Другие виды применения сульфата кальция

Ц научно-технический и производственный журнал

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