Advances in Science and Technology Vol. 69

Abstract: Geopolymer is an inorganic alumino-silicate product that shows good bonding properties. Geopolymer binders are used together with aggregates to produce geopolymer concrete which is an ideal building material for infrastructures. A by-product material such as fly ash is mixed together with an alkali to produce geopolymer. Current research on geopolymer concrete has shown potential of the material for construction of reinforced concrete structures. Structural performance of reinforced concrete depends on the bond between concrete and the reinforcing steel. Design provisions of reinforced concrete as a composite material are based on the bond strength between concrete and steel. Since geopolymer binder is chemically different from Ordinary Portland Cement (OPC) binder, it is necessary to understand the bond strength between geopolymer concrete and steel reinforcement for its application to reinforced concrete structures. Pull out test is commonly used to evaluate the bond strength between concrete and reinforcing steel. This paper describes the results of the pull out tests carried out to investigate the bond strength between fly ash based geopolymer concrete and steel reinforcing bars. Beam end specimens in accordance with the ASTM Standard A944 were used for the tests. In the experimental program, 24 geopolymer concrete and 24 OPC concrete specimens were tested for pull out. The concrete compressive strength varied from 25 to 55 MPa. The other test parameters were concrete cover and bar diameter. The reinforcing steel was 500 MPa steel deformed bars of 20 mm and 24 mm diameter. The concrete cover to bar diameter ratio varied from 1.71 to 3.62. It was found from the test results that the failure occurred by splitting of concrete in the region bonded with the steel bar, in both geopolymer and OPC concrete specimens. Comparison of the test results shows that geopolymer concrete has higher bond strength than OPC concrete. This suggests that the existing design equations for bond strength of OPC concrete with steel reinforcing bars can be conservatively used for calculation of bond strength of geopolymer concrete.

Abstract: A geopolymer produced from Jordanian kaolinite is described in this work. The aim is to produce low environmental impact materials from local raw materials. In this paper the emphasis is on the general characteristics of the material and on its durability. With the used kaolinite, specimens with compressive strength of 41 MPa under dry conditions and 23 MPa under immersed water conditions were obtained. The durability under environmental conditions was good.

Abstract: Construction and demolition waste (CDW) is a by-product of construction and demolition activity. It consists mostly of inert and non-biodegradable material such as concrete, plaster, metal, wood, plastics etc. CDW is priority waste in the E.U. due to the increased quantities and volumes that are produced. While retrievable items such as brick, wood and metal wires are recycled, concrete, masonry tile and ceramic waste, accounting for more than 60% of CDW, are not being currently recycled. The main objective of this study is to develop a process for obtaining new building materials from CDW using low temperature geopolymerisation in alkaline environment. The two major fractions of the CDW which are not currently being recycled are concrete, mortars, masonry and rubbles for one side and ceramic tile, mosaic and bricks for the other. The major constituents of the first fraction are SiO2 and CaO along with minor concentration of Al2O3 and Fe2O3, mostly crystalline. The major constituents of the latter are SiO2 and Al2O3 and comprise crystalline as well as glassy constituents. The aluminosilicate fraction of both fractions will actively participate in the reaction and for the obtaining of ASH gel (A= Al2O3, S = SiO2, H = H2O), which is the main binding phase. Any deficiency (quantity) in chemical constituents will be compensated by addition of suitable material, e.g., Al2O3 can be compensated with a source of alumina which will be added for alkaline activation reaction. The remaining non aluminosilicate portions such as iron oxide and others will act as filler material. The final product is a very hard ceramic like product. These products can be used for civil engineering applications such as pavement blocks, precast concrete blocks, retaining walls, in general the same use as plain concrete.

Abstract: The main causes of rock degradation in stone buildings are discussed and the current methods of recovering damaged stones are summarized. The Alkaline Activation seems to present a great potential to deal with particular cases of damaged stones resulting mainly from fracture incidents provoked by physical actions, where the global substitution of the stone itself is not considered. A practical case of recovering granite on the windows frames of a beautiful chalet to be intended for the Municipal Archives at Vila Real is described, in what is considered to be the first experiment of this technique in recovering building stone.

Abstract: One of the most promising applications of geopolymers is their use as waste encapsulating matrix. These binders are indeed compatible with aqueous waste streams and capable of activating several chemical and physical immobilization mechanisms for a wide range of inorganic waste species. Several works have investigated the immobilization of cations, mainly heavy metals or radioactive wastes, but very few studies are taking counterions, namely anions, into account. The aim of this work is to experimentally investigate the impact of anions with different valences on the materials’ properties in regard to the requirements of an industrial process at ambient or slightly elevated temperature: among others setting time, maximum achievable compressive strength or resistance to leaching. The modifications caused by the introduction of monovalent and divalent anions, such as sulphate and nitrate, are also monitored in term of mineralogy, porosity and microstructure. Their immobilization seems to be related to the advancement of geopolymerization reaction. On another hand, depending on the alkali ions used in the activation solution, the anionic species considered may also enhance the precipitation of some zeolites.

Abstract: In this work, wastewater from Teva Pharmaceutical Industries Ltd., which comprises several organic and inorganic compounds, was solidified in a geopolymer matrix. The addition of wastewater to the polymerization mixture of fly ash based geopolymers yielded a high compressive strength of 50-75 MPa that is similar to that of wastewater-free geopolymer. The leaching of organic compounds from the matrix was examined and it was found to be negligible, about 0.2%wt, and comparable to the amount that leached from a geopolymer matrix made without wastewater. The results indicate that the immersion temperature and the time of immersion have negligible influences on carbon leaching.

Abstract: Geopolymers as an alternative binder system gains growing attention in research and development. Outstanding technical properties like high strength, high acid resistance, or high temperature resistance can be unerringly achieved. Thus geopolymers are not only suitable for the development of building products, but are also interesting binder systems for ceramic applications. Besides the technical performance of geopolymers, which is well investigated, only limited scientific knowledge exists about the environmental sustainability of geopolymers [1]. Due to the wide range of suitable raw materials and hence resulting, different geopolymer compositions for distinct application fields a generally statement about the environmental implications cannot be addressed to geopolymers. A more detailed analysis and assessment is needed, to provide more diversified statements.

Abstract: In this study different geopolymers have been investigated and characterized as potential biomaterials. The work presents exhaustive FT-IR, SEM/EDS and X-Ray studies of two geopolymer formulations, where water content, water to solid content and curing conditions have been varied during mixing stage, maintaining constant the ratios among Na-Al-Si. The amorphous matrix is typical of sodium aluminosilicates, as shown by the FT-IR spectra. The presence of zeolitic phases has been observed by XRD at the surface of the material while the main matrix was characterized by amorphous aluminosilicate phases. The compressive strength of all the compositions was higher than 50 MPa. In order to study their bioactivity, samples of the studied materials were soaked in a simulated body fluid (SBF). The bioactivity of the synthesized geopolymers was shown by the formation of a layer of hydroxyapatite on the surface of the materials by using the SEM.