Easy Evaluation Method of Self-Compactability of Self-Compacting Concrete

Transcription

1 Easy Evaluation Method of Self-Copactability of Self-Copacting Concrete Masanori Maruoka 1 Hiroi Fujiwara 2 Erika Ogura 3 Nobu Watanabe 4 T 11 ABSTRACT The use of self-copacting concrete (SCC) in construction is designed to iprove the durability of the structure, by creating as far as possible a coletely filled, voidless and faultless concrete state. However, even with SCC, achieving coplete self-copaction is extreely difficult. Therefore, before construction starts, the self-copactability of SCC is exained using, for exaple, a real-size odel forwork in order to deterine whether the self-copactability in the construction is adequate. However, the cost of such exainations is high, and so a cheaper and easy exaination ethod is desirable. In this study, we investigated an evaluation ethod for evaluating the self-copactability of SCC easily by varying several paraeters of concrete, ortar and construction properties, such as the rheological properties of ortar, unit volue of coarse aggregate of concrete, and state of obstacle distribution in the forwork. Our cost-effective and siple ethod enabled pressure force loss of flowing SCC around the ostacles to be evaluated in a forwork. We believe that this ethod will contribute to the iproveent of durability of constructions using self-copacting concrete. KEYWORDS Self-copacting concrete, Self-copactability, Rheology, Force loss of flowing concrete Utsunoiya University, Faculty of Architecture and Civil Engineering, Utsunoiya, Japan, Phone , Fax , aruoka@cc.utsunoiya-u.ac.jp Utsunoiya University, Faculty of Architecture and Civil Engineering, Utsunoiya, Japan, Phone , Fax , fhiroi@cc.utsunoiya-u.ac.jp Utsunoiya University, Faculty of Architecture and Civil Engineering, Utsunoiya, Japan, Phone , Fax , t042807@cc.utsunoiya-u.ac.jp Utsunoiya University, Faculty of Architecture and Civil Engineering, Utsunoiya, Japan, Phone , Fax , t063433@cc.utsunoiya-u.ac.jp

2 1 INTRODUCTION If concrete can be poured copletely and is voidless and faultless, the durability of a concrete structure will not deteriorate through the influence of, for exaple, carbonation and freezing and thawing action. However, producing such a state of concrete is difficult and thus deterioration of the durability reains an iportant consideration. The use of self-copacting concrete (SCC) in construction is designed to iprove the durability by creating, as far as possible, a copletely filled, voidless and faultless concrete state. There are currently two estiation ethods of the self-copactability of SCC. One involves the SCC filling test using the real-size odel forwork odeled fro a real structure and deterining whether or not the forwork is filled copletely or not. The other is a siulation ethod of nuerical analysis. To date, few investigations of the forer ethod have been conducted, and the latter ethod requires odel paraeters of the structure as well as paraeters of the fresh SCC properties and ix content design of SCC which are very difficult to obtain. Moreover, nuerical analysis does not always provide sufficient inforation. In this study, we aied to develop an easy ethod for evaluating the degree of self-copactability of SCC using a odel experient involving a visualization ethod of concrete. In this experient, we use a odel of self-copacting concrete that aintains the sae fluidity, such as slup flow. The iportant paraeters for this evaluation are unit content of coarse aggregate, rheological properties of ortar, and interspace size of obstacles in the forwork. We alter these paraeters and evaluate selfcopactability via the pressure loss paraeter in the odel experient. The results of investigations of this new ethod are presented and discussed. 2 WHAT IS PRESSURE OSS? We define pressure loss for use in the evaluation of self-copactability of SCC as follows. In the case of SCC flowing in the channel for with steel bars as obstacles (see Figure 1), the strea line of SCC is changed around the obstacle. If unit coarse aggregate content is sall, for exaple, the unit absolute volue of coarse aggregate is less than about / 3, SCC flow is continued and flows around the obstacle slowly, and there is little height difference between the upstrea and downstrea surfaces of SCC that is bounded by the obstacle (Case (a) of Figure 1). If unit coarse aggregate content of SCC is very large, for exaple, the unit volue of coarse aggregate is ore than about / 3, and if segregation occurs, SCC flow stops due to coarse aggregate blockage around the obstacle, such that SCC in the section containing coarse aggregate is changed by the effect of the obstacle (Case (b) of Figure 1). In this case, a difference in surface height is observed. Flow Direction Interspace size: Obstacle (Steel bar) Diaeter: D Iage of concrete flowing channel Flow Direction H in H out Case (a): evel of surface heights are alost sae, H in H out. Obstacle Figure 1. Differences in surface height between upper and lower sections divided by an obstacle.

3 Pressure loss is calculated by Eq. (1) using the difference in surface height. Then, we considered that the pressure loss value can be used as an index of the evaluation of self-copactability. ΔP=ρ g Δh (1) 3 OUTINE OF EXAMINATIONS 3.1 Exaination Method Measuring Method of Pressure oss In this exaination, we use a odel for ade of clear acrylic sheet with obstacles ade of pipe, as shown in Figure 2. The ethod, also shown in Figure 2, is as follows. [1] The gate of the for closes and Tank A is filled with odel concrete (see section 3.3 for details). [2] The gate opens and concrete flows out fro Tank A to Tank B through the obstacle interspaces. [3] The flow velocity becoes slow and eventually stops. [4] We then easure the height of the concrete surface in Tanks A and B, and calculate the height difference between the Δh, and calculate the pressure loss value ΔP using Eq. (1). The ain paraeters for this exaination are interspace size of obstacle: (by changing diaeter of obstacles; 4 types, 21, 24, 26 and 30 diaeter) and coarse aggregate volue of odel concrete: Xv (3 types, 0.26, 0.30 and 0.34). Figure 2. Details of odel for and easuring ethod of height difference Δh between surface of SCC in Tanks A and B Visualization Test to Investigate Flow State Next, we try to estiate the changing coarse aggregate volue divided into two sections by the obstacle. The ethod is shown in Figure 3. The increase in the volue of coarse aggregate Xv was then easured and calculated. A still iage was taken, and Area 1 and Area 2 were defined as shown in Figure 3. Iage processing showed the coarse aggregate in white in the iage, and the ratios of the white area (contained in Area 1) to Area 1 and the white area (contained in Area 2) to Area 2 were defined as S 1 and S 2, respectively. Then, the difference in the volue ratio of coarse aggregate

4 between upstrea of and downstrea of the obstacle ΔXv and the increased coarse aggregate ratio Xv is given by Eq. (2), S1 S 2 2S Δ Xv = Xv, 1 Xv' = Xv + ΔXv = Xv (2) S + S S + S where ΔXv is the increase in the volue ratio of coarse aggregate, Xv is the initial unit volue ratio of coarse aggregate, S 1 is the area ratio of coarse aggregate in Area 1, S 2 is area ratio of coarse aggregate in Area 2, and Xv is the volue ratio of coarse aggregate increased in Area Materials Used Figure 3. Method of easuring coarse aggregate area using iage analysis. In these exainations, we ust be able to view the coarse aggregate particles, which cannot be done using real SCC. Therefore we use odel concrete containing water and a viscosity agent typically used for concrete aterial as odel ortar, and processed lightweight aggregate (density: 1.35 g/c 3, axiu size: 15 ) as odel coarse aggregate. The odel ortar is therefore alost clear, allowing the distribution of the odel coarse aggregate to be observed in the odel forwork. In order to capture the coarse aggregate oveent data easily, we paint the coarse aggregate yellow. 3.3 Mix Content of Concrete Mass ratios of the viscosity agent content of the odel ortar were 12.5, 15 and 17.5 %. In these conditions, ortar flow with no vibration is alost around 250. The unit volue content of the coarse aggregate was 0.26, 0.30 and Exaination Results Measuring Pressure oss Figure 4 shows the relationship between pressure loss ΔP and interspace size. These results show that in the case of sall, ΔP increases ore than in the case of large, and this relationship is siilar to that obtained for odel ortar with a different Xv and viscosity. This eans that under the condition of sall and large Xv, it is difficult for the odel SCC to flow around the obstacle, and it is considered that the resistance force of the steel bars disturbs and decreases the flow of odel SCC, resulting in an increase in ΔP. In the case in which high viscosity ortar is used, ΔP decreases; the occurrence of contact and friction between the coarse aggregate particles decreases, and this has a large effect of the stress transfer echanis.

5 3.4.2 Flow State of Coarse Aggregate In every case we observed that the easured coarse aggregate volue of the upstrea section divided by the obstacle was greater than the downstrea section. The reasons are thought to be that the strea line of SCC flow around the obstacle changes fro being linear to curved and coarse aggregate particles cannot ove easily because of the obstacle disturbance and thereby restrict particle oveent in the interspaces and the upstrea section, aking the SCC flow ore difficult. In the downstrea section, however, where there is no obstacle, the coarse aggregate volue is saller. We consider the phenoenon of SCC passing around the obstacle to be an iportant echanis when describing increasing pressure loss. Measured Pressure oss: P (Pa) Figure 4 Relationship between interspaces size of obstacle and easured pressure loss ΔP 4 BUIDING UP THE THEORETICA AND EXPERIMENTA FUNCTIONS TO DESCRIBE INCREASING PRESSURE OSS 4.1 Modeling the Mechanis of Generating and Increasing Pressure oss To investigate the echanis odel of generating and increasing pressure loss, we consider the phenoenon of increasing pressure loss when SCC flows through the obstacle interspaces as follows. [1] Coarse aggregate in flowing SCC is delayed in front of obstacles When SCC flows through the forwork with steel bars, the flow line of SCC changes fro being linear to curved as a result of having to flow around the steel bars, and oveent of coarse aggregate contained in the SCC around the steel bars is obstructed and the flow velocity of coarse aggregate is decreased. We considered one of the reasons causing this phenoenon is coarse aggregate volue change in the SCC. We considered the change to be caused by original coarse aggregate volue Xv, increased volue of coarse aggregate Xv, interspace size, ortar viscosity, and yield stress. Considering these paraeters, we show the relationship between Xv and Xv /Xv in Figure 5 left side and the equation to explain the phenoenon in Eq. (3) [Kaneatsu et. al. 1999]. Xv' = ΓXv + 1 Xv (3) In the case of sall, the slant Γ of the relationship is larger than for large. We introduce the idea of relative interspace size r that is defined in Figure 6 right side and Eqs. (4) and (5). We will verify these relationships later. b Γ = a r (4), r = (5) + D

6 where a and b are paraeters including the rheological properties of ortar, is the interspace size (), and D is the diaeter of the obstacle (). [2] Volue of coarse aggregate in front of the obstacle increases Coarse aggregate particles accuulate in front of the obstacles due to the phenoenon described in [1]. [3] Change in the stress transfer echanis inside SCC We consider that, inside the SCC, the sheer stress σ and shearing stress τ act on the surfaces of the coarse aggregate particles, as shown in Figure 6 left side. In the case of SCC having low volue of coarse aggregate particles and high volue of ortar, shearing stress has no influence on sheer stress. However, as the volue ratio of coarse aggregate particles to ortar increases, coarse aggregate particles can coe into contact with each other easily. As a result, we consider that the echanis of the stress transfer odel changes and the relationship between σ and τ becoes linear, as shown in Figure 6 center. [4] Increases in yield stress of SCC and sheer stress at the surface of coarse aggregate particles The shearing stress increases with increasing sheer stress. Thus, the deforation resistance force of SCC also increases, and the yield stress of SCC increases. [5] Increasing pressure loss When SCC flows through the interspaces between the steel bars, it sees a balance of dynaics is arrived at around the steel bars, as shown in Figure 6 right side and Eq. (6). Furtherore, it sees that the force acting on the steel bars fro the SCC is related to the decrease in pressure around the steel bars, as described by Eq. (6) for estiating pressure loss. This forula shows that pressure loss increases as the yield stress increases. Thus, we have derived a odel explaining the increasing pressure loss echanis by eans of the above steps [1]-[5]. 2D ΔP = τ c D + (6) where τ c is the yield stress of SCC, ΔP is the pressure difference present in the interspaces between the steel bars, D is the diaeter of the steel bars, and is the distance between adjacent steel bars. In the next section, we will explain about the increase coarse aggregate volue echanis described in [1], and investigate it through exaination. Figure 5. Concepts of relationship between original coarse aggregate volue Xv and relative Xv /Xv (left side), and relationship between relative interspace size r and Γ which is the slant of the relationship between Xv /Xv and Xv (right side).

7 Coarse aggregate Shearing stress: τ Sheer stress: σ Mechanis of particle friction odel Mechanis of viscous drag Steel bar (like Bingha fluid) Concrete flow Sheer stress : Figure 6. Concepts of sheer and shearing stress (left side), change in stress transfer echanis (center), and dynaics odel of the steel bar interspaces (right side). 4.2 Investiagation of the Model Relationship between Xv /Xv and Viscosity of Mortar The left side of Figure 7 shows the relationship between Xv /Xv and Xv, as calculated by iage analysis. Xv increases with narrowing, and increasing Xv /Xv is saller when high viscosity ortar is used. The right side of Figure 7 shows the relationship between Γ and r. Curves indicate the approxiate curves of plots in these relationships for each ortar viscosity case applied. In the case of sall r, Γ decreases with increasing ortar viscosity. This suggests that the increase in coarse aggregate volue is controlled partly by increase in ortar viscosity. Equations in this figure show the approxiate curves of the relationship between Γ and r, and are shown in Eq. (7) r Γ = r r ( η ) = 0.507Pa s ( η = 0.545Pa s) ( ) η = 0.748Pa s (7) The left side of Figure 8 shows the relationship between ortar viscosity and coefficient a, b. In this test, there are only three types of ortar viscosity, but they have linear relationships. These are shown in Eq. (8). a η , b η (8) = = This allows us to explain the increase coarse aggregate is partly due to the influence of ortar viscosity. Figure 7. Relationship between relative increase in coarse aggregate volue Xv /Xv and Xv (left side) and relationship between Γ that is the slant of the relationship between Xv /Xv and Xv, and relative interspace size r (right side).

8 Figure 8. Relationship between coefficients of a, b and ortar viscosity (left side) and relationship ratio of yield stress of concrete and ortar τ c /τ and original coarse aggregate volue of SCC Xv (right side) Relationship between Yield Stress of Concrete and Mortar and Coarse Aggregate Volue In this exaination, we used a concrete viscoeter, and investigated the relationship between relative yield stress of concrete and ortar τ c /τ and coarse aggregate volue Xv. The results are shown in Figure 8. Each relationship has essentially a straight relation, like Eq. (9), and the slants of the lines increase with increasing ortar viscosity. Thus, there is a relationship between coefficient c and ortar viscosity as shown in Eq. (10). τ c τ = cxv +1 (9), c 6.816η (10) = Calculating and Estiating Pressure oss We consider that pressure loss can be estiated easily fro the aforeentioned relationships between the rheological paraeters of ortar, coarse aggregate volue, interspace size and diaeter of the obstacle. Equation (11), which has been published previously [Maruoka, et al. 2005], is as follows, ( ) + 1 τ = 0.553(2R0 ) , η = t , τ c τ = η Xv, 2D Δ P = ( cxv + 1) τ, c = 6.816η (11) D+ where, τ is the yield stress of ortar (Pa), η is the viscosity of ortar (Pa*s), R 0 is the radius of ortar flow with no vibration (), and t 14 is the ortar flow through tie of the J 14 type funnel (s). 5. COMPARISON OF MEASURED AND ESTIMATED PRESSURE OSS Figure 9 shows the coparative results of easured pressure loss and estiated pressure loss. For low pressure loss (under 200 Pa), the results are siilar. However, in certain cases they are dissiilar, i.e., when ortar viscosity is low and interspace size is narrow. The reason that the odel generates pressure loss is in the condition of using low viscosity ortar, where there is large friction between the coarse aggregate particles and odeling this is difficult. Hereafter, we will attept to iprove the precision of the odeling.

9 Figure 9. Coparison of easured and estiated pressure loss. 6 CONCUSIONS We attepted to estiate the self-copactability of SCC by considering the pressure loss phenoenon. We proposed an easy ethod for estiating pressure loss, using the rheological paraeters of ortar and concrete, coarse aggregate volue and diaeter of the obstacle. Using a visualization ethod to ake clear the state of concrete flowing through a channel with obstacles, we detected changes in coarse aggregate volue and observed differences between upstrea and downstrea SCC flow. On the basis of the rheological proprties and soe derived equations, we estiated the pressure loss, finding that the easured value of pressure loss and estiated value was generally siilar, enabling us to estiate pressure loss and self-copactability easily. REFERENCES Kaneatsu, M., Nagai, H., Oh Sang-Gyun, Noguchi, T. & Toosawa F., 1999, Evaluation of Passing Ability of Self-Copacting Concrete Part1.Evaluation Method, Suaries of technical papers of Annual Meeting Architectural Institute of Japan. A-1, Materials and construction, Maruoka, M., Fujiwara, H., Watanabe, Y., Iwasaki, A., & Fujie, Y., 2005, Experiental investigation of estiating ethod of pressure loss of self-copacting concrete pass through the gaps between rebars, Journal of aterial, japan society of civil engineers, concrete structures and paveent, No.795/V-68,