Mechanical properties and structural performance of preplaced aggregate concrete members | |
| Author | Coo, Michael Lim |
| Call Number | AIT Diss no.ST-16-02 |
| Subject(s) | Precast concrete construction Concrete--Curing Cement Building materials |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Structural Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. ST-16-02 |
| Abstract | In casting Preplaced Aggregate Concrete (PAC), coarse aggregates are preplaced into formworks then grouts are injected to fill up voids, enabling coarse aggregates to occupy much greater volume than conventional casting methods. This method basically depends on the ability of the grout to fill up voids and the size of the voids, which are dependent on the workability of the grout and the coarse aggregate shape and gradation. The increase of these aggregates in the concrete volume could also alter concrete performance during service. Usual design measures to increase the filling ability of grouts are to increase water and superplasticizer content of grout mixtures, which could cause bleeding and segregation. Stiff grout mixtures on the other hand could cause cavities in the final PA concrete due to unfilled voids. In both instances, strength properties of PAC would be affected. By lowering the water content in grout mixtures, bleeding and segregation could be minimized, but workability will also be reduced. Loss in workability could be compensated by the use of mineral admixtures such as fly ash, but the extent of compensation should be studied especially on PAC grouts that are mostly extended with sand. The effects of fly ash replacement and sand content on PA grout properties are studied, along with the effects of coarse aggregate gradation on PAC mixtures. Limestone fillers are also studied as cement fillers on PAC grouts to further reduce cost. A factorial design of experiment is used to quantify effects of each factor on PAC properties. Reinforced beam and slab specimens are then casted and load tested using these PAC mixture proportions to prove that this concrete material studied is suitable for use in actual structures. Results has shown that fly ash could compensate for the workability loss on low w/c grouts containing sand, which could reduce flow times as much as 25% on mixtures containing 40% fly ash and 1:1 sand to binder ratio. Hardened strength properties of low W/B ratio PAC is mainly affected by the levels of fly ash and sand present in the grout mixture, not coarse aggregate gradation. The inclusion of an optimized proportion of sand and fly ash in PAC improves strength up to 80%, 60% and 40% increase in compressive, tensile and flexural strength respectively, compared to lean grout mixtures. Limestone powder has also shown to be an effective grout filler that has minimal effect on grout fluidity, but at the expense of mechanical strength. Structural members cast using PAC have shown identical behavior and load bearing capacities with conventionally cast concrete. It is concluded that the inclusion of sand and fly ash in PAC mixture improves strength and economy of PAC. Limestone powder is an effective filler to reduce material cost when economy is desired over high material strength (>30 MPa fc’). Using optimized PAC on structural members reduces concrete material cost as much as 30% at the same structural loading performance. |
| Year | 2015 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. ST-16-02 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Structural Engineering (STE) /Former Name = Structural Engineering and Construction (ST) |
| Chairperson(s) | Pennung Warnitchai;Thanakorn Pheeraphan; |
| Examination Committee(s) | Raktipong Sahamitmongkol;Chai Jaturapitakkul; |
| Scholarship Donor(s) | AIT Fellowship; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2016 |