Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xi, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 112-118).

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 124-130).

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 79-83).

The production of high-performance concrete having all-rounded high performance has been promoted for the last few decades. Meanwhile, environmental concerns have quested for minimizing cement consumption to reduce carbon footprint. However, contradictory requirements are often imposed on the mix parameters in order to satisfy all the required performance attributes and environmental limitations. The addition of inert fillers such as limestone fines (LF) is a promising way to overcome these difficulties. In this thesis, the packing density and overall performance of mortar and concrete containing different amounts of LF are investigated. The test results revealed that blending of fine aggregate with LF or with both LF and cement could significantly increase the packing density because the LF and cement particles are much smaller than the aggregate particles and are thus able to fill into the voids between the aggregate particles. However, LF with similar fineness as cement has no filling effect for increasing the packing density when added to cement to a mortar mix in which the powder content is already enough to fill the voids between aggregate particles. Its filling effect is contributed mainly by filling into the paste to increase the paste volume. In fact, the addition of LF to mortar would slightly decrease the packing density, significantly decrease the water film thickness (WFT) and significantly increase the paste film thickness (PFT). The actual effects of LF volume on the packing density, WFT and PFT are dependent on the cement paste volume. In-depth analysis of the test results showed that the apparently complicated effects of the LF volume are caused by the corresponding changes in the WFT and PFT of the mortar. The overall effects of LF are dependent on the net outcome of the decrease in WFT and the increase in PFT due to the addition of LF. The addition of LF would increase the flow spread when the WFT is relatively large as the decrease in WFT has smaller effect than the increase in PFT, increase the cohesiveness when the LF volume is relatively small as the decrease in WFT has greater effect and increase the early strength provided the WFT would not become too small. However, the addition of LF would always decrease the flow rate because the decrease in WFT always has greater effect than the increase in PFT. Finally, the possible use of LF as cement paste replacement to reduce cement paste volume is studied. From the correlation of the ultimate shrinkage strain to the cement paste volume and W/C ratio, and to the concrete strength and cement paste volume, it may be concluded that cement paste replacement by the addition of LF would reduce the shrinkage of concrete by both decreasing the cement paste volume and increasing the concrete strength. Moreover, since the reduction in cement paste volume would allow less cement to be used, this would also lead to the production of concrete more ecological. More research on this possible usage of various inert fillers with different fineness is recommended. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains xi, 79, [30] p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 75-79).

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains x, 177 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 134-141).

The present recommendations of the ACI-ASCE Committee 352 for the design of ductile moment resistant beam to column connections limit the joint shear stress to γ√f'(c), where the factor γ is a function of the joint geometric classification and the loading condition. The value of compressive strength f'(c) used in the above expression should not exceed 6000 psi. This limitation causes considerable difficulty in the design of high-strength concrete frames. An experimental study of twelve large-scale exterior beam to column subassemblies was completed at The University of Arizona. The specimens were subjected to cyclic inelastic loading. The variables studied were the concrete compressive strength (8.1, 10.7, and 13.6 ksi), the joint shear stress (1100 and 1400 psi), and the degree of joint confinement provided in the form of closed ties. Although high-strength concrete is more brittle than normal-strength concrete, the study showed that frames constructed of high-strength concrete can perform satisfactorily in earthquakes zones when attention is given to proper detailing of joints. The flexural strength ratio, degree of joint confinement, development length of bars, and joint shear stress are all very important factors to be considered in the design process. The maximum permissible joint shear stress suggested by ACI-ASCE Committee 352 was modified for frames constructed with high-strength concrete. The proposed joint shear stress drawn from test results does not affect the factor γ which depends on the joint type and its geometric classification. Therefore, in the absence of any further data about interior joints, the proposed joint shear limit for high-strength concrete can be used for all types and geometric classifications of joints. Furthermore, new requirements for joint confinement were presented to ensure ductile behavior of frames. It is important to note that current Recommendations for joint confinement, which were developed for normal-strength concrete, cannot be satisfied for high-strength concrete frames. The hysteresis response of specimens tested and other normal-strength concrete specimens tested by different investigators were compared in terms of their energy absorption capacity. This comparison was essential to alleviate concern about the lack of ductility of high-strength concrete. Favorable results were obtained. This research is important for practitioners to gain more confidence using high-strength concrete for structural design applications especially in seismic zones.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 149-155).

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

It is generally very difficult to produce high-performance concrete having concurrently high strength, high durability, high workability and high dimensional stability. This is because low water content is required to achieve high strength and high durability, high water content and large paste volume are required to achieve high workability, and low cement content and small cement paste volume are required to achieve high dimensional stability. One way of overcoming such conflicts is to add fillers to increase the packing density of concrete so that the amounts of water and paste needed to fill voids could be reduced. In this study, the use of fillers to improve the packing density and performance of concrete is investigated by measuring the packing density and overall performance of cement paste and concrete mix samples with different types and amounts of fillers added. The packing density results revealed that finer fillers are more effective in improving the packing density for releasing more excess water (water in excess of that needed to fill voids) to lubricate the solid particles. Moreover, triple blending of two fillers of different fineness with cement can better increase the packing density than double blending of just one filler with cement. On the other hand, the workability, strength and dimensional stability results showed that the addition of condensed silica fume, fly ash microsphere or superfine cement could improve the overall workability-strength performance of cement paste through increasing the packing density of the cementitious materials, while the addition of condensed silica fume, fly ash or limestone fine coeuld improve the overall dimensional stability-strength performance of concrete through decreasing the cement content or cement paste volume. Hence, the incorporation of fillers to improve the packing density opens up the possibility of using ultra-low W/CM ratio and ultralow paste volume to produce an ultrahigh-performance concrete. However, despite increases in packing density and excess water, the addition of fillers does not always improve the workability. Generally, the addition of fillers would more significantly increase the workability at low W/CM ratio and less significantly increase or even decrease the workability at high W/CM ratio. In-depth analysis indicated that both the excess water and solid surface area have great effects on the rheology. In this regard, a parameter called water film thickness (WFT), which is defined as the average thickness of water films coating the solid particles and may be determined as the excess water to solid surface area ratio, is proven to be the key factor governing the rheology. Therefore, it should be the WFT rather than the packing density that should be maximized in the mix design of high-performance concrete. The addition of fillers would increase both the excess water and solid surface area. If the proportional increase in excess water is larger than the proportional increase in solid surface area, the WFT would increase, but if otherwise, the WFT would decrease. To increase the WFT, a filler that can significantly increase the packing density without excessively increasing the solid surface area is the best choice. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy