Emission of carbon dioxide gas has been a source of major concern for the construction industry. To curb this emission, geopolymer concrete has been deemed as a potential alternative in the recent studies. Previous research also indicates that silica and fibers provide strength benefits to ordinary Portland cement concrete OPC. This study was undertaken to recognize the benefits of adding silica and basalt fibers in Class F fly ash based geopolymer concrete and comparing it with OPC concrete. One OPC and four Geopolymer mixtures were prepared. The results show a tremendous potential of using geopolymer concrete in place of OPC concrete with Nano silica proving to be the most advantageous. Nano silica provided 28% increase in compressive strength, 8% increase in resistivity when compared with normal Fly ash based geopolymer concrete. The SEM analysis of geopolymer concrete indicates that nano silica improved the compactness of concrete providing a dense microstructure.

In the construction of buildings and infrastructures, high resistance materials are used due to current design requirements, concrete being one of the main materials used in the execution of these projects whose cement content is limited to obtaining an economic concrete and of minimum retraction. This limitation requires the use of new additions such as Nano Silica (NS), which due to its nanometric structure is used as a partial replacement for cement, producing an increase in strength in concrete. The present investigation studies the partial replacement of the NS in the cement to determine its behavior in compressive strength, diametric compressive strength, water permeability coefficient. The results indicate that with an addition of 0.225% of NS the compressive strength and splitting tensile strength are increased and the water permeability coefficient decreases, all of them compared to a conventional concrete.

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Yes / This paper aims to evaluate the influence of surface area and amount of nano silica (NS) on the performance of concrete with different water/binder (w/b) ratios. For this purpose, 63 different mixes were produced using three NS having three differentsurface areas (52, 250 and 500 m2/g) and w/b ratios (0.4, 0.5 and 0.6). Compressive strengths , workability, water absorption and the microstrcture of concrete mixtures were measured and analysed. and the optimum ratio for each type was determined. The results indicated that the performance of NS particles in concrete is significantly dependent on its amount and surface area as well as w/b ratio. As the w/b ratio increased, a better performance was observed for all types of NS used, whilst NS having 250m2/g surface area was found to be the most effective. The optimum amount of NS ranged from 2 to 5%, depending on NS surface area. / The full-text of this article will be released for public view at the end of the publisher embargo on 15 May 2020.

Yes / Limited information related to the application of nano silica in recycled aggregate concretes has been available in the literature. However, investigations on the effect of nano silica on the bond performance of reinforcement embedment length in recycled aggregate concrete have not been conducted yet. Therefore, the present study aimed at investigating the bond strength for recycled aggregate concretes incorporating nano silica under different levels of corrosive environments. The experimental work consisted of testing 180 pull-out specimens prepared from different mixtures. The main parameters studied were the amount of recycled aggregate (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), embedment length (5 and 13Ø) as well as reinforcement diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. Finally, the experimental results were compared with the existing models. Experimental results showed that the bond performance between un-corroded steel and RCA concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of a small quantity of NS (1.5%) showed between 8 and 21% bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence was observed with the increase of corrosion periods, reflecting the improvement in corrosion resistance. NS particles showed a more effective role with RCA concretes rather than conventional concretes in terms of enhancing bond and corrosion resistance. Therefore, it was superbly effective in recovering the poor performance in bond for RCA concretes. By doubling the content of NS (3%), the bond resistance slightly enhanced for non-corroded samples, while its influence becomes more pronounced with increasing RCA content as well as exposure time to corrosion.

Very limited research studies have been conducted to examine the behaviour of rubberised concrete (RuC) with nano silica (NS) and addressed the acoustic benefits of rubberised concrete. The current research investigates the effect of incorporating colloidal nano silica on the mechanical, thermal and acoustic properties of Rubberised concrete and compares them with normal concrete (NC). Two sizes of rubber were used RA (0.5 – 1.5 mm) and RB (1.5 – 3 mm). Fine aggregate was replaced with rubber at a ratio of 0%, 10%, 20% and 30% by volume, and NS is used as partial cement replacement by 0%, 1.5% and 3%. A constant water to cement ratio of 0.45 was used in all concrete mixes. Various properties of rubberised concrete, including the density, water absorption, the compressive strength, the flexural strength, splitting tensile strength and the drying shrinkage of samples was studied as well as thermal and acoustic properties. Experimental results of compressive strength obtained from this study together with collected comprehensive database from different sources available in the literature were compared to five existing models, namely Khatib and Bayomy- 99 model, Guneyisi-04 model, Khaloo-08 model, Youssf-16 model, and Bompa-17 model. To assess the quality of predictive models, influence of rubber content on the compressive strength is studied. An artificial neural network (ANN) models were developed to predict compressive strength of RuC using the same data used in the existing models. Three ANN sets namely ANN1, ANN2 and ANN3 with different numbers of hidden layer neurons were constructed. Comparison between the results given by the ANN2 model and the results obtained by the five existing predicted models were presented. A finite element approach is proposed for calculating the transmission loss of concrete, the displacement in the solid phase and the pressure in the fluid phase is investigated. The transmission loss of the 50mm concrete samples is calculated via the COMSOL environment, the results from the simulation show good agreement with the measured data. The results showed that, using up to 20% of rubber as fine aggregate with the addition of 3% NS can produce a higher compressive strength than the NC. Experimental results of this research indicate that incorporating nano silica into RuC mixes enhance sound absorption and thermal conductivity compared to normal concrete (NC) and rubberised concrete without nano silica. This work suggests that it is possible to design and manufacture concrete which can provide an improvement to conventional concrete in terms of the attained vibro-acoustic and thermal performance. / Libyan Ministry of Higher Education

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-02-05T08:03:54Z No. of bitstreams: 2 Dissertação - Tiago Ferreira Campos Neto - 2015.pdf: 3471853 bytes, checksum: 35e5a04973ea3b1be09afd99f6dc94f1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-02-05T08:06:27Z (GMT) No. of bitstreams: 2 Dissertação - Tiago Ferreira Campos Neto - 2015.pdf: 3471853 bytes, checksum: 35e5a04973ea3b1be09afd99f6dc94f1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2016-02-05T08:06:27Z (GMT). No. of bitstreams: 2 Dissertação - Tiago Ferreira Campos Neto - 2015.pdf: 3471853 bytes, checksum: 35e5a04973ea3b1be09afd99f6dc94f1 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2015-06-12 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The rheological properties... / As propriedades reológicas...

Made available in DSpace on 2014-12-17T14:07:08Z (GMT). No. of bitstreams: 1 ManoelIQJ_DISSERT.pdf: 1658589 bytes, checksum: 30023fa8ec2e11231777b5b0249ad3cc (MD5) Previous issue date: 2013-05-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The oil wells cementing is a critical step during the phase of well drilling, because problems during the operation of slurry pumping and an incomplete filling of the annular space between the metal casing and the formation can cause the slurry loss. Therefore, the slurry adopted in primary cementing an oil well must be properly dosed so that these problems are avoided during its pumping. When you drill a well in a weak rock formation requires even more careful, because should be a limit of hydrostatic pressure exerted during cementation, that does not occur rock collapse. With the objective of performing the cementing of a well whose formation is weak or unconsolidated are employed lighter slurries. Thus, this study used slurries with sodium silicate and nano silica in concentrations of 0,1; 0,4; 0,7 e 1,0 gpc, in which the slurries with nano silica showed the rheological parameters higher concentrations of up to 0.7 gpc and for concentration of 1.0 the slurry with sodium silicate obtained the highest values, remaining above the limits for application in fields, mainly wells with low fracture gradient, because a significant increase in viscosity may result in an increase in pressure pumping in operations of secondary cementations. Furthermore, there was no decrease in strength with increasing concentration of additive. Then, it is possible use of these additives to formulate Lighter slurry / A cimenta??o de po?os de petr?leo ? uma das etapas mais criticas durante a fase de perfura??o de um po?o, pois problemas durante a opera??o de bombeio da pasta e um preenchimento incompleto do espa?o anular, entre o revestimento e a parede do po?o, podem causar a perda do mesmo. Portanto, a pasta adotada na cimenta??o prim?ria de um po?o de petr?leo deve ser calculada adequadamente para que sejam evitados estes problemas durante seu bombeamento. Ao se perfurar um po?o em uma forma??o rochosa fraca requer-se, ainda, mais cuidado, pois, em geral, deve existir um limite de press?o hidrost?tica exercida durante a cimenta??o, para que n?o haja o colapso da forma??o. Com o objetivo de se realizar a cimenta??o de um po?o cuja forma??o ? fraca ou inconsolidada s?o empregadas pastas leves. Desta forma, neste trabalho foram utilizadas pastas com silicato de s?dio e nano s?lica em concentra??es de 0,1; 0,4; 0,7 e 1,0 gpc, onde as pastas com nano s?lica apresentaram os par?metros reol?gicos superiores at? a concentra??o de 0,7 gpc e para a concentra??o de 1,0 gpc a pasta com silicato de s?dio obteve os maiores valores, ficando acima dos limites estabelecidos para aplica??o em campos, principalmente em po?os com baixo gradiente de fratura, pois o aumento significativo da viscosidade pode resultar no incremento da press?o de bombeio em opera??es de recimenta??o. Al?m disto, n?o foi observado em decr?scimo de resist?ncia mec?nica com aumento de concentra??o dos aditivos. Sendo poss?vel utiliza??o destes aditivos para formula??o de pastas leves

The current research project mainly aims to investigate the corrosion resistance and bond performance of steel reinforced recycled aggregate concrete incorporating nano-silica under both normal and corrosive environmental conditions. The experimental part includes testing of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica (1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm). Different levels of corrosion were electrochemically induced by applying impressed voltage technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the corrosion level in addition to the ultimate bond, failure modes and slips occurred. Experimental results showed that the bond performance between un-corroded steel and recycled aggregate concrete slightly reduced, while a significant degradation was observed after being exposed to corrosive conditions, in comparison to normal concrete. On the other hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal and RCA concretes under normal conditions. However, much better influence in terms of bond and corrosion resistance was observed under advancing levels of corrosion exposure, reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in recovering the poor performance in bond for RCA concretes. More efficiency was reported with RCA concretes compared to the conventional concrete. The bond resistance slightly with a small amount of corrosion (almost 2% weight loss), then a significant bond degradation occurs with further corrosion. The influence of specific surface area and amount of nano silica on the performance of concrete with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced with three different types of colloidal NS having various surface areas and particle sizes. The results showed that the performance of concrete is heavily influenced by changing the surface area of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2 /g achieved the highest enhancement rate in terms of compressive strength, water absorption and microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4 m2 /g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is affected by its particle size as well as water to binder ratio. The feasibility of the impact-echo method for identifying the corrosion was evaluated and compared to the corrosion obtained by mass loss method. The results showed that the impact echo testing can be effectively used to qualitatively detect the damage caused by corrosion in reinforced concrete structures. A significant difference in the dominant frequencies response was observed after exposure to the high and moderate levels of corrosion, whilst no clear trend was observed at the initial stage of corrosion. Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models were able to predict the bond strength with a high level of accuracy, which was confirmed by conducting a parametric study. / Higher Education Institute of the Libyan Government