الفهرس 
Introduction & Literature reviewOnly 14 pages are availabe for public view
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Abstract
Chapter7
Summary and Conclusions
Cementitious materials are the most widely used for plastering of the building envelopes; however, they possess low thermal resistivity, low tensile strength and ductility which leading to cracking with time. The aim of this work was to develop lightweight cementitious composites with improved thermal resistivity and acceptable/reasonable mechanical performance to be used for energy efficient building envelopes. In order to overcome the weaknesses/brittleness of cement pastes, fibers are incorporated into cementitious matrix, the use of this microfiber reinforcement leads to the improvement of mechanical properties of cement based materials. This microfiber inclusion assists to delay the development of micro-cracks but not help to stop or terminate their initiation. The addition of nano particles has been considered to improve the resistance to crack initiation of cement based materials and to enhance the mechanical performance of the fiber reinforced cement composites. Fibers in hardened cement paste and mortar have physical effects. Such as, they tend to increase the stress at which the matrix starts to crack (strengthening effect), improve the strain capacity or ductility of the inherently brittle and modify crack development in terms of reducing crack width and average crack spacing.
In contrast to the fibers, the nano particles have physical and chemical effects, Due to its ultrafine size, NMK particles act as fillers, fill the voids between cement grains (physical packing) and improve the microstructure of NMK modified cement bulk pastes; furthermore it may improve the interfacial zone between the fiber and the partly hydrated cement grains. Due to its high active/amorphous silica content, NMK participates in the pozzolanic reaction, i.e. it reacts with the free lime which liberates during cement hydration resulted in the production of additional amounts of calcium silicate hydrate (CSH) which is the strength responsible phase with a strong hydraulic character.
For the production of lightweight thermally resistive cementitious materials, the use of lightweight aggregates with low thermal conductivity has been considered to provide enhanced thermal insulation characteristics.
The role of the developed lightweight thermally resistive cementitious materials in minimizing cooling energy consumption inside residential buildings has been investigated
The results obtained from these experiments have led to the following conclusions:
• The use of natural fibers is very effective in enhancing the flexural strength of cementitious surface composites; an enhancement of flexural strength by about 82% of the plain cement paste at 2% fiber content was obtained.
• NMK was more beneficial as mineral additives to cement; NMK improves the microstructure and provides additional enhancement in flexural strength of FRCC, an increase with nearly 67% of FRCC was obtained when replacing WPC by 10% NMK.
• NMK reduces the capillary absorption coefficient of FRCC and resulted in more dense and compact structure.
• The degradation of fibres in a high alkaline environment of cement matrix adversely affects the mechanical and durability properties of natural fibre-reinforced cement composites. The use of NMK in natural fibre-reinforced cement composites has reduced the alkalinity of cement matrix by consuming calcium hydroxide during the pozzolanic reaction, hence improving the durability of natural fibres in the composite.
• Nanostructured lightweight fiber reinforced cementitious surface composites (NLWFRCC) with enhanced thermal resistance, high solar reflectivity and reasonable flexural strength have been developed utilizing natural fibers, nano metakaolin and expanded perlite.
• In contrast to previous works reported in the literature, the developed NLWFRCC are characterized with very low thermal conductivity which means that they possess very high thermal resistivity.
• Even at 70% perlite, the flexural strength of NLWFRCC is 2.9 MPa which is a significant value and might satisfies the prescribed mechanical requirements.
• Perlite particles have increased the solar reflectivity of NLWFRCC by about 33% as compared with composite with no perlite.
• NMK is very effective in enhancing the mechanical performance and minimizing the capillary water absorption of high volume EVM white cement composites, replacing 70 vol% cement.
• Partial replacement of EVM by 10% NMK has significantly enhanced the compressive and flexural strengths by about 57 and 59%, respectively.
• NMK has considerably reduced the capillary water absorption of high volume EVM white cement composites, replacing 70 vol% cement by about 74% at 28 days of hydration.
• NMK has led to a great improvement in the microstructure of EVM blended cement.
• The developed lightweight vermiculite cement composites are characterized by low density and thermal conductivity while have an enhanced mechanical strength, i.e. are fully recommended for energy efficient building envelopes.
• NLWFRCC are found to be very helpful in reducing the cooling energy consumption of a reference residential building located in Cairo, Egypt by about 33 %.
Following recommendations can be made after extensive literature review and current study:
• The degradation mechanisms of natural fiber indicate the effect of alkalinity of the cement pore solution on the decomposition of its structure. Further investigation of the natural fiber degradation in cement matrices is necessary.
• Chemical treatment is economical and easy to apply and therefore deserve to be studied further. At present, our linen fibers have not been physically or chemically treated; chemical treatments of natural fibers may improve durability with less potential hazards, Further investigation on durability characteristic is necessary
• The fire resistance and sound insulation characteristics of the developed LWCC might be investigated in future work.