OLD BUILDINGS RESTORATION TECHNIQUE. Dr-Ing JK Makunza University of Dar es Salaam 18 th May 2011

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1 OLD BUILDINGS RESTORATION TECHNIQUE Dr-Ing JK Makunza University of Dar es Salaam 18 th May 2011

2 Introduction Zanzibar is an archipelago made up of Zanzibar and Pemba Islands. It is located in the Indian ocean, about 40 km from the Tanzanian coast, and 6 south of the equator. Zanzibar Island shown in Figure 1, locally known as Unguja, is 97 km long and 32 km wide, occupying a total area of approximately 1683 square kilometers. Fig. 1

3 Stone Town Stone Town is the old city and cultural heart of Zanzibar Town. It is a place of winding alleys, bustling bazaars, mosques and grand stone houses whose original owners viewed with each other over the extravagance of their dwellings (refer Fig. 2). Figure 2: Historic buildings in Zanzibar

4 Stone Town contains around 1709 Stone Masonry Buildings and associated structures that have architectural styles which reflect special culture, that has brought together and homogenized different elements of cultures from Africa, Middle East, Far East and Europe.. Stone Town has great historical value and has become tourist attraction as such, this township is benefiting Zanzibar people in terms of culture and economy. (a) Middle East design (b) Far East design Figure 3: Designs from different parts of the world

5 CONSTRUCTION TECHNOLOGY AND MATERIALS The buildings are up to three stories high The walls are massive, t = 500 to 1000 mm in thickness, constructed of rubble stones randomly set in a thick lime based The walls have very shallow foundation of about 500 mm deep and in most cases, walls were constructed without any foundation. The mangrove poles are used to support the floors and roofs The floor slab is usually in form of bays of around 1200 mm wide and utilizes the arch principle in which the forces are transmitted to the beams then to the thick masonry walls.

6 CURRENT PROBLEM Stone Town is a World Heritage; this means, it is a conserved area. One of the principles of conservation is to restore the buildings as they were, using similar materials and design. Looking at current state of most repaired historical buildings in Stone town it is quite clear that the repair attempts made have not been effective.(see Figs. 4 and 5). Observing the facade of the historical buildings in Stone Town, Zanzibar, stone units appears to be in good condition while mortar (joint mortar, plaster, render) present an extremely advance deterioration condition (see Figures 4 and 5).

7 Figure 4: Recently repaired building, but with delaminated plaster

8 Figure 5: Deteriorated building

9 OBJECTIVES The main objective of carrying out the study was firstly, to seek for restoration materials which have the same structural properties as the original ones so that they provide good functionality in the old buildings, making the buildings more durable with minimum intervention. Secondly, by matching the original materials techniques closely, the repair materials would age in a similar manner as the original materials. The significance of this study has been to ensure that, these historic buildings continue to exist.

10 THE PRACTICAL APPROACH Two methods were employed 1. Visual assessment 2. Sampling of materials (a) From existing historical buildings. - Old materials (mortar and coral stones) (b) New materials that are currently used for restoration on site (mortar, lime, sand and stones) 3. Laboratory tests of the samples

11 Tests Tests were done in order: To determine chemical properties of the materials sampled from old buildings (stone and mortar). To establish compressive strength of existing mortar and lime stones. To establish compressive strength of new prepared mortar at the age of 7,14 and 28 days. To determine the compressive strength of limestone collected from the currently existing quarries. To conduct sand gradation test existing in the historic buildings. To conduct sand gradation test of the currently used sand for restoration purposes.

12 Results Table 1: Analysis of major element in Old Mortar in Historic buildings and New Mortar Sample ID Historical mortar Current mortar MgO Al 2 O 3 SiO 2 Na 2 O K 2 O SO 3 CaO Sample ID TiO 2 Historical mortar Fe 2 O 3 Cl P 2 O 5 Cr 2 O 3 MnO LOI Current mortar

13 Results Table 2: Chemical Test Results for Coral-stones and Lime stones Sample ID MgO Al 2 O 3 SiO 2 SrO K 2 O SO 3 CaO Coral stone Lime stone < Sample ID TiO 2 Fe 2 O 3 Na 2 O P 2 O 5 ZrO 2 LOI Coral stone Lime stone < < The chemical compositions are according to the established standards for each case, however there is a difference between the old and new materials.

14 Sieve Size [mm] GRADING OF SANDS The grain size distribution in soil is determined by performing Sieve Analysis 70 Grading Curves age Passing historical mortar current mortar grading

15 Absorption [] Water Absorption Test Results Water Absorption Coral Stone Limestone Sample No Figure 6: Water absorption of coral-stone and limestone

16 SPECIMENS FOR TESTING. Samples of 70 x 70 x 70 mm in size were cast, after hardening they were kept in normal room temperature and humidity in a water bath as shown in Figure.7. Figure 7: Cubic mortar samples

17 Density [kg/dm3] Density Densities of Coral stone and Limestone 3 Limestone 2 1 Coral stone Sample No. Figure 8: Densities of stones

18 Desnsity [kg/dm3] Density of Moratrs 2 Old Mortar 1.5 New Mortar Sample No. Figure 9: Density of mortars

19 Compressive Strength [N/mm2] Tests for Compressive Strength The stones as well as the mortars were tested for the compressive strengths using a universal testing machine. The results are as follows: Compressive Strength of Stones Limestone Coral stone Sample No. Figure 10: Compressive strength result of coral and limestone.

20 Compressive Strength [N/mm2] Compressive Strength of Mortars Old Mortar 0.5 New Mortar Sample No. Figure 11: Compressive strength of mortars

21 Discussions on the Results Chemical properties are similar to the standards for in stones and mortars of current and historical buildings. However the materials are somehow different from each other. Sieve analysis show that sands which are used in current mortar are finer than the sands which were used in historical mortar Compressive strength values of lime stone are greater than coral stone. Compressive strength of current mortar will continue to develop strength until 15 months due to slow rate of chemical reactions, therefore due to time limit it is difficult to compare this strength. Historical mortar show good result in compressive strength, because maximum compressive strength of mortar start from 0.45 up to 0.95 N/mm 2..

22 Recommendations As such, according to the study conducted, it is recommended that in case of mortar, in order to get good strength in current mortar, it is important to change the type of sand to the one which has coarser particles than the one in current use, because currently it need more lime since it has finer particles For stones, it is recommended to use lime stone than coral stone because lime stone have more strength than coral stone. Also coral stone absorbs more water due to its high porosity property which cause damage to the buildings than lime stones