Abstract

Historical stone monuments and buildings are lost due to salt induced decay. This paper deals with a method, electro-desalination (ED), in which an electric DC field is applied to the infected stones. The method utilizes that ions are transported (electromigrating) in the pore solution in the electric field. In the experimental work here, sandstone prisms were spiked with NaCl to high concentrations prior to ED. During the application of current, the Cl ions are electromigrating into a poultice at the anode, and Na ions into a poultice at the cathode. Damaged stones are often fragile and cracked, and the focus of this paper is to investigate experimentally if the salts are removed effectively from the stone parts next to a crack. In the lab experiments performed, a crack was cut half through the rectangular sandstone prisms perpendicular to the electric field. The results showed no delay on the ED processfrom the crack. All through the stone, very low concentrations of Na and Cl were reached. The concentration were even lower than the concentrations before the spiking. This finding of effective desalination around a crack is important, as it means that during ED, the poultice with electrodes can be placed around the cracked and fragile surfaces, and thus further damage from physical contact between poultice and fragile stone can be avoided.

Abstract

Water repellents are widely applied directly to the outer surfaces of existing buildings to increase the hydrophobicity and durability of historic facades. Nevertheless, there is little control over the initial moisture content inside masonry and boundary conditions in practice. The fluctuating temperature and moisture content of a wall are inevitable when applying the treatment under natural climatic conditions, therefore the efficiency under realistic application approaches may not be as optimal as in the lab. This research aims to understand how application circumstances affect the hydrophobic efficiency of a siloxane-based water-repellent solvent on sandstone. Samples with different moisture content were treated and cured under different temperature to simulate various field climate conditions in practical applications. The experiments indicate that application temperature and relative humidity have little effect on water-repellent efficiency. The water-repellent product is also effective on saturated walls.

Abstract

Technical experts in construction industries are trying to improve the quality, ease of using materials in different forms, and increasing structure performance. However, in the changing cost of each item, quality of works could be sacrificed. In Ethiopia, the practice of using alternative ingredients to produce materials was observed weak in some scenarios. It was because ignoring the right procedures to perform the required material requirements for construction materials. It is known that Ambo area has a scarcity of natural sand or rivers sand which can be extracted from the river bed. Notably, if available, the quality is not good due to the presence of silt and clay. Once it used, it adversely affects the structural integrity of concrete structures. The primary objective of the research is to evaluate the suitability of Ambo Sandstone Fine Aggregate (ASFA) as an alternative replacement of river sand in normal concrete production. Samples extracted from Senkele and Aleltu quarry sites of Ambo Area. Results showed that fine aggregates from Senkele quarry site indicated 14.28% silt content, while from the Aleltu quarry site indicated 12.28% silt content, all of which exceeded 6% based on Ethiopian Standard Specification. It means the samples must be rejected or appropriately washed before use as a part of a concrete mix. After performing the procedure to remove silt content, it found out that the silt content reduced to 5.3%, less than the allowable maximum of 6%. Hence, Ambo Sandstone Fine Aggregates (ASFA) are suitable for concrete mix production and strength determination. There were nine samples of concrete cubes prepared and tested at 7th, 14th, and 28th days for concrete compressive strength with a mix ratio of 1:2:3 and water to cement ratio of 0.50. Based on the laboratory test results with full replacement of river sand by Ambo Sandstone Fine Aggregate (ASFA), the mean compressive strengths at 7th day was 16.61 MPa, while at the 14th day was 19.62MPa, and at 28th day was 25.59 MPa. It means at 28th day; it satisfied the minimum requirement for C-25 grade concrete. Likewise, the cost of production of the fine aggregate of the Ambo Sandstone quarry site is 140 ETB per cubic meter, while the price of river sand from Legeher Market is 300 ETB-400 ETB per cubic meter. Therefore, Ambo Sandstone Fine Aggregate (ASFA) is cheaper than the river sand. However, it must be given emphasis that the Ambo Sandstone Fine Aggregates must wash thoroughly before use in construction projects.

Abstract