Self-compacting concrete: mix proportioning, properties and its flow simulation in the V-funnel

Self-compacting concrete (SCC) is a type of concrete, which flows under the sole influence of gravity up to leveling, air out and consolidates itself without any external compaction energy. It was a response to the lack of qualified skilled workers at the construction sites and a solution for the accomplishment of durable concrete structures. Self-compactability of a concrete mix is widely affected by the characteristics of ingredients and their proportions. Thus, it becomes necessary to develop a successful procedure for mix proportioning of SCC. The heuristic nature of the early mix proportioning methods motivated researchers to carry out extensive research on the rheological properties of SCC that has significantly improved the proportioning of SCC mixes. A rigorous proportioning method for SCC based on sound physical principles was proposed. However, such a method produces a bewildering array of mixes that reach the target plastic viscosity but does not give any practical guidelines on how to choose the most appropriate mix and does not explicitly impose compressive strength as a design criterion. These shortcomings were overcome in this work by developing a new mix proportioning method. Indeed, practical guidelines in the form of design charts were provided for choosing the mix proportions that achieve a target plastic viscosity in the range 3 to 15Pa s (the lower limit varies with target cube compressive strength) and a target cube compressive strength in the range 30 to 80MPa. To verify the proposed mix design method, an experimental validation was performed on a series of SCC mixes in both the fresh and hardened states. Three sets of SCC mixes were prepared jointly with other two PhD students (Abo Dhaheer, 2016; Al-Rubaye, 2016). These mixes are designated A, B, and C for the low, medium and high paste to solids ratios, respectively. (Note that mixes designated A and C were contributed by the other two named PhD students). Tests on these mixes conclusively proved the validity of the mix design approach in the sense that all the mixes met the self-compactability criteria and achieved the desired target plastic viscosity and cube compressive strength. vii Although SCC has passed from the research phase into the real application, the differences in its composition (i.e. higher paste volume and lower coarse aggregate volume) from normal vibrated concrete (NVC) raise concerns among researchers about its fracture behaviour. Thus, an experimental study has been carried out to investigate in detail the role of several composition parameters of SCC mixes on their fracture behaviour differing by the coarse aggregate volume, paste to solids ratio (p/s) and water to cementitious material (w/cm) ratio. The specific fracture energy and the tension-softening diagram of a concrete mix are the most critical parameters that describe its fracture behaviour as they form a basis for the evaluation of the load carrying capacity of cracked concrete. First, the size-dependent fracture energy (Gf) has been determined using the RILEM work-of-fracture test on three point bend specimens of a single size, half of which contained a shallow starter notch (notch to depth ratio=0.1), while the other half contained a deep notch (notch to depth ratio=0.6). Then the specific size-independent fracture energy (GF) was calculated using the simplified boundary effect formalism in which a bilinear diagram approximates the variation in the fracture energy along the unbroken specimen ligament. Finally, the bilinear approximation of the tension softening diagram corresponding to GF has been obtained using the non-linear hinge model. Predicting the flow behaviour in the formwork and linking the required rheological parameters to flow tests conducted on the site will help to optimise the casting process. A Lagrangian particle-based method, the smooth particle hydrodynamics (SPH) is used to model the flow of SCC mixes in the V-funnel. An incompressible SPH method was employed to simulate the flow of such a non-Newtonian fluid whose behaviour is best described by a Bingham-type model, in which the kink in the shear stress versus shear strain rate diagram is first appropriately smoothed out. The basic equations solved in the SPH are the incompressible mass conservation and momentum equations. The simulation of the SCC mixes emphasised the distribution of larger aggregates particles of different sizes throughout the flow in the 3-dimensional V-funnel configuration. The capabilities of this methodology were validated by comparing the simulation results with the V-funnel tests carried out in the laboratory

Utilizing CFRP Sheet for Strengthening Extended Concrete Beams

This research investigates the behavior of extended reinforced concrete beams that have been enhanced using CFRP at the extension points. Five reinforced concrete beams with measurements of 2500 mm in length, 150mm in width, and 260mm in height were built and extended in different types. The studied cases included varied CFRP strengthening schemes for the splice joints. The findings conclude that the inclusion of horizontal stirrups on the complete top of the beam produced comparable results to those of the reference beam. Additionally, the spliced beams glued at their lateral faces and strengthened by vertical CFRP laminates provided a marginal increase in their ultimate loads. The results also showed that the strengthening with carbon fibers exhibited lower crack width than the reference beam in general

Investigating factors affecting feasibility study of construction projects in iraq

The views at the construction field emboss that construction parties are looking for a higher benefit during implementing aspects of any project. The feasibility study is one of the serious and significant matters in construction sectors as well as in other engineering fields as it has a high impact on investment decision-making. To gain rigorous decisions from decision-makers or contractual parties (client, consultant, and contractor), there is a need for valuable feasibility studies in any construction project. This paper aims to study the influence of some identified factors on feasibility studies as well as the extents of priorities of various feasibility studies. In this paper, the critical factors that have an impact on sequences of initial feasibility studies during the lifecycle of a construction project were identified as well as the associated studies (legal, environment, marketing, technical, managerial, schedule, financial and economic). In this study, 12 factors were identified, analyzed, and thoroughly discussed to have recommendations of their impact on initial feasibility in construction projects in Iraq via a questionnaire survey and a series of expert interviews conducted in Iraq. The Analytical Hierarchy Process (AHP) as a multi-criteria decision support system was adopted to examine the weight of each factor. In addition, an analysis by the Relative Importance Index (RII) was carried out to rank eight types of feasibility studies in terms of their perceived importance. The results of AHP indicated that the local shortage of database about the feasibility study was the most critical factor. Indeed, RII's result showed that all kinds of feasibility for construction projects in Iraq are not adopted by the client. In fact, the economic feasibility study was the most popular than others

Patricia Douglas Interview, December 20, 1976

Patricia Douglas offers her definition of what the University of Montana is and what a liberal arts education is. She details the University’s main sources of funding, and explains why the Montana University System made its largest funding request, as of 1976, due to inflation. Douglas summarizes trends in enrollment at the University and clarifies why forecasting enrollment is difficult to predict. She emphasizes the University’s importance in her life, and the opportunities that she feels the institution presents to young Montanans and non-traditional students. Douglas details her role as Assistant to the President, and her work with President Bowers communicating with Montanans about how the University could serve them.https://scholarworks.umt.edu/umhistory_interviews/1024/thumbnail.jp

Influence of mix composition and strength on the fracture properties of self-compacting concrete

Self-compacting concrete (SCC) has undergone extensive investigations that have led to confidence in its fresh and hardened properties, yet its composition variations raise concerns as to its fracture behaviour. This paper presents the results of an experimental study on fracture behaviour of SCC mixes differing by the coarse aggregate volume, paste to solids ratio (p/s) and water to binder (or cementitious material (w/cm )) ratio. First the size-dependent fracture energy (Gf) has been determined using the RILEM work-of-fracture test on three point bend specimens of a single size, half of which contained a shallow starter notch (notch to depth ratio = 0.1), while the other half contained a deep notch (notch to depth ratio = 0.6). Then the specific size-independent fracture energy (GF) was calculated using the simplified boundary effect formalism in which the variation in the fracture energy along the unbroken specimen ligament is approximated by a bilinear diagram. Finally, the bilinear approximation of the tension softening diagram corresponding to GF has been obtained using the non-linear hinge model. It is found that GF and the critical crack opening (wc ) are dominated by the coarse aggregate volume in the mix and the mix grade. The larger the coarse aggregate volume (or the smaller the paste to solids ratio) the larger are both the mix toughness (GF) and the critical crack opening (wc ). However, the higher the mix grade the larger is the mix toughness (GF) but the lower is the critical crack opening (wc)

Proportioning of self-compacting concrete mixes based on target plastic viscosity and compressive strength: Part II experimental validation

A companion paper by the authors described the mix design procedure and gave several examples on the use of the design charts. This paper is concerned with the experimental validation of the mix design procedure on a series of SCC mixes in both the fresh and hardened states. A series of SCC mixes that contained different volumetric ratios of paste to solid phases were prepared using the design charts. All these mixes were extensively tested in the fresh state using the slump cone, J-ring, L-box, and V-funnel apparatus. These tests proved conclusively the validity of the mix proportioning method in the sense that all the mixes satisfied the self-compacting criteria and achieved the desired target plastic viscosity and compressive strength