VOL. 101, NO. 3. r~(~n- MAY.nmE2~ MATERIAL JOURNAL

Transcription

1 VOL. 101, NO. 3 r~(~n MAY.nmE2~ MATERIAL S JOURNAL

2 ,-, 1 n '., ACI MATERI'ALSJOURNAL ' Title no. 101-M23, ' TECHNIC n :. d ". 'ti Evaluation of Static Stability of Self-Consolidatins Concrete y. by Joseph Assaad, Kamal H. Khayat, and Joseph Daczko In ls s, in ~. Proven test methods to assess the resistance oi self-consolidating concrete (SCC) to segregation and surface settlement during the plastic stageare requiredto ensureuniformpropertiesoi the hardened material. A test program was undertaken to compare the suitability oi a number oi test methods ior assessing the static stability oi (:rr T1-.n 'WInt1-.,.,r/(' ;",,..I,,r/n n"nlj1nt;",o (,Jlrfn,..p ('pttlpwlpnt and settlement can weaken the qual between aggregate and cement paste w impenneability and mechanical prope embedded reinforcement that is espec structural elements can also be weakened

3 Joseph Assaad is a PhD candidate al the Université de Sherbrooke, Quebec, Canada. His research interests include rheology and fonnwork pressure of self-consolidating concrete. ACI member KamaI H. Khayat is aprofessor of civil engineering at the Universitéde Sherbrooke. He is a member of ACI Committees 234, Silica Fume in Concrete; 236, Material Science of Concrete; 237, Self-Consolidating Concrete; and 552, Geotechnical Cement Grouting. His research interests include self-consolidating concrete, rheology, and concrete repair. ACI member Joseph Daczko is Group Manager of Concrete Technology, Research and Development Department, Master Builders, Inc., Cleveland. Ohio. He received his BA from John Carroll University, University Heights, Ohio. He is a member of ACI Committees 236, Material Science of Concrete, and Chair of 237, Self-Consolidating Concrete. His research interests include self-consolidating concrete. based systemsduring the donnant period of cement hydration. The method relies on monitoring the differences in electrical conductivity along a sample of a cement-based material as a function of time to interpret internal water movement and segregation. The results obtained from this method show that 0.74%, respectively, with a Blaine specific m2fkg. A continuously graded crushed limes with a nominal partic1esize of 14mm and a \\ ceous sand were used. The coarse aggregatt fineness moduli of 6.4 and 2.5, respective specific gravities were 2.71 and 2.69, and th were 0.4 and 1.2%, respectively. A polycarboxylate-based HRWRA with s of 1.1 and solid content of 27% was used. A e VMA with a specificgravityof 1.12and a solid was employed. All mixtures incorporated a based set-retarding agent to minimize fiuid testing. The admixture had a specific gravit) solid content of 31%. Mixture proportions The concrete mixtures were proportioned w ("{'\ntpntc {'\.f ":ts2'\..nrl '\00 ),"', 3 ''T'~ 1~ 1 \ A 1.

4 Following the end of mixing, the slump flow, rheological parameters, surface settlement, column segregation, and electrical conductivity were determined. These tests are described as follows. 1. Slump flow test- The test consists of determining the mean diameter of concrete on the base plate after the complete stoppage of the flow. An ordinary slump cone as per ASTM e 143is used. The test evaluates the capability of concrete to deform under its own weight and enables the assessment of both the rate of deformability and the maximum deformation capacity. 2. Concrete rheometer test-an available cornmercially concrete rheometer was used to determine rheological parameters.10 The test involves recording the torque of an H-shaped impeller rotating in a planetary motion to maintain a given impeller angular speed. The testing protocol consisted of gradually increasing the mixing speed up to a maximum velocity. Subsequently, the speed is reduced in settlement from 0.72 to 0.6%, and then to O concrete made with 0.40 w/c and a slump flc 4. Column segregation test- This test this study and consists of casting cor measuring 660 rnm in height and 200 m determining the variation in the relati, coarse aggregate at four sections along t The PVC tube is divided into four sect height. A leak -free joint is provided bet~ that they can be easily uncoupled. Bef test, the concrete is vertically consolidatt: 20 rnm-diameter rodding bar. The concft: for 15 mino After removing each sectio top, the concrete is weighed and the mor a 5 rnm sieve to retain coarse aggregat dried to obtain a near surface-saturated clr) The coarse aggregate content is then det the four samples The coefficient.... of var..

5 S e :1 { s Following the end of mixing, the slump flow, rheological parameters, surface settlement, column segregation, and electrical conductivity were determined. These tests are described as follows. 1. Slump flow test- The test consists of determining the mean diameter of concrete on the base plate after the complete stoppage of the flow. An ordinary slump cone as per ASTM e 143 is used. The test evaluates the capability of concrete to deform under its own weight and enables the assessment of both the rate of deformability and the maximum deformation capacity. 2. Concrete rheometer test-an available cornmercially concrete rheometer was used to determine rheological parameters.10 The test involves recording the torque of an H-shaped impeller rotating in a planetary motion to maintain a given impeller angular speed. The testing protocol consisted of gradually increasing the mixing speed up to a maximum velocity. Subsequently, the speed is reduced in ~_+ ': :I ~..r settlement from 0.72 to 0.6%, and then to concrete made with 0.40 w/c and a slump f 4. Column segregation test- This te this study and consists of casting C( measuring 660 rnm in height and 200 ] determining the variation in the relat coarse aggregate at four sections along The PVC tube is divided into four se. height. A leak-free joint is provided be' that they can be easily uncoupled. Be test, the concrete is vertically consolida 20 rnm-diameter rodding bar. The conc] for 15 mino After removing each secti. top, the concrete is weighed and the mo a 5 rnm sieve to retain coarse aggreg~ dried to obtain a near surface-saturated dj The coarse aggregate content is then de the four samples. The coefficient of va

6 TEST RESULTS ANO OISCUSSION To evaluate the repeatability of the various responses, the L mixture was batched five times (Table 2). The results obtained show that the COY of the various responses varies between 0.9% (slump flow test) and 13.3% (g rehological parameter). The g and h values exhibited the highest relative errors corresponding to 28.5 and 22.9%, respectively. Table 3 surnmarizes the test results of the 16 tested mixtures. The values representing the L mixture were taken as the mean results obtained from the repeatability tests A --G L ~ L L-VMc\ _L_VMc\ Rheological parameters All torque-angular velocity responses following the Bingham model with correlatioj values greater than A typical example e four SCC mixtures with 615:t 15 rnm slump j Fig. 1. As can be seen, the g and h value~ mixtures prepared with 385 kglm3 of cement those made with 500 kg/m3 of cementot, related to changes in volume of cement paste ~ into account. The reduction of cement cont4 increase in relative volume of coarse aggre, paste ratio (Table 1). This can, therefore, r, viscositydue to greater internalfrictionbetwee particles. A secondary effect may be due HRWRA dosage incorporated in mixtures pn lower cement factor (385 kglm3) compared made with 500 kglm3 of cemento When concentration, some of the HRWRA can rem

7 lear tr2 s of in for ith ena ken ) an md- ~her gate ater the ete igh on, For example, by comparing the L-VMA and L-VMA mixtures, the g and h values decreased by 1.6 N.m and 7 N.m.s when the w/c decreased from 0.47 to 0.42, respectively. This is due to additional water content that lubricates the mixture and reduces the flow resistance and viscosity. Furthermore, it is to noted that the rheological parameters are affected by the level of consistency. For higher slump flow values, the g and h parameters are shown to decrease. In the case of the L- VMA and H-VMA mixtures,such reductioncorresponds to 1.2 N.m and 10 N.m.s, respectively. Dynamic stability tests As previously mentioned, the V-funnel flow time, JRing, L-box, U-box, and pressure bleed tests were used to evaluate the dynamic stability of SCC in the first part of this study.2 Generally speaking, mixtures prepared with 500 kg/m3 of cement were found to exhibit better passing ability compared ' u_j ~.'-,-,oc' ~ ~ ~_. 'T't..: 1 :1 Khayat, Ghezal, and Hadriche14have of coarse aggregate has a significan1 settlement.at relativelylow bindercon1 the increase in coarse aggregatevolum in surfacesettlement.on the other han< aggregate content can lead to a settlement in SCC mixtures with rel:: binder (500 kg/m3). The use ofvma reducedthe surface~ the case of the L and 385-( where a reduction of 0.27% of settlem this relatively lean SCC mixture wa~ This can be attributed to the increas( mixture resulting from the VMA bin the mixing water.1except for the 385- mixtures, the surface settlement incre in the slump flow. For example, the : shown to increase by 0.13% for the '1O&: f\ A"7 TT """,ira ~:" ~_...1..~~

8 reduced to 0.44 mmih when the VMA was incorporated in both mixtures. Therefore, both initial rate of settlement and maximum settlement are higher for mixtures made with a higher volume of coarse aggregate and a greater HRWRA dosage. The incorporation of VMA also reduces the rate of settlement as well as the settlement magnitude. The relationship between the maximum surface settlement and the initial rate of settlement is plotted in Fig. 5 (R2 of 0.73). As shown in Fig. 6, no significant relationship was established between the rheological parameters and the surfacesettlement.the R2 values were 0.17 and 0.12 for the g andh with respectto the settlementamplitude,respectively. ~ 1.6 f I 11 Slump flow = 715 :i: 15 mm Column segregation test The segregation index lseg values are suiru Concrete made with 500 kglm3 of cem highest lseg values varying between 2 and : hand, mixtures containing 385 kg/m3 of c relatively high g and h parameters ext values ranging between 1.3 and 4.3%. between the lseg value and rheological paj in Fig. 7 (R2 values of 0.67 and 0.71 for respect to the lseg values, respectively). Hi can limit coarse aggregate segregation, lower lseg values. This can alter flowabil lead to a poor level of self-consolidation. Con value and plastic viscosity are considerably lo most likely OCCUf, resulting in high lsegvalm segregation defined arbitrary from the van, generated from this study are plotted in Fi of the g and h parameters. These regions..."'1 _~ A + L:1"r1 1,..."., Al,.,., PTTI r

9 from 2.8 to 4.1% and 2 to 3.5%for the and VMA mixtures, respectively. Even though the column segregation test offers relevant information conceming the effect of mixture composition on the relative concentration of coarse aggregate along a sample of concrete, the determination of the Ise is time consuming and may not be suitable for frequent quagtycontrol at the job site. Consequently, a simplified method for evaluating the segregation is adopted by comparing only the top and bottom sections of the column segregation (Table 3). The results show that the simplified Isegvalues are greater as compared with those resulting from ilie index calculated from the four sections of the column. This is due to the fact that the COY increases as the spread between the results increases. The relationship between the simplified IseSvalues and the ones calculatedfrom the four sectionsis givenidfig. 10(Jil ofo.8l). From the foregoing surface settlement and column C''''M<>lTM1nnrbt~ it ~h()111c1he emnhasized that the results of consolidation and water migration. e bottom pair of electrodes, the conductivi time, whichis consistentwith thedecrease( and increase in solid fraction that reduce ( an elapsed period of time correspondin toplbottom pair of electrodes reach conductivity,indicating the stoppage of fi and sedimentation of solid partic1es, commencement of chemical precipita1 setting take precedence from this time To quantitatively evaluate bleeding, overall homogeneity of the suspension, 2 ~o 4 ~ 3j 11 R

10 based on the electrical conductivity data were employed.15 They are surnmarized in Table 4 and are calculated as described as follows. Bleeding index lb is the cumulative area between the conductivity values obtained from the top pair of electrodes and the mean conductivity of all electrode pairs, considered between the initial and peak values, divided by the elapsed time required to reach the peak conductivity. A highly stable system would have a bleeding index nearing zero. Table 4-Results of bleeding, segregation, and homogeneity evaluated from electrical conductivity test Bleeding Segregation Homogeneity index lb index 1s index 1H L L- VMA H Segregation index IS is the cumulative art bottom pair of electrodes and the mean of CO the electrode pairs, considered between the i values, divided by the elapsed time require peak value. A highly stable system would yiei index nearing zero. The homogeneity index 1H is calculated as : area between the mean of top two pairs an bottom two pairs of electrodes considered f value to the end of observation period, dividec time). A perfectly homogeneous system WO value of 1.0. The homogeneityindexesof SCC mixtureswi slump flow are compared in Fig. 13. The H-VMA mixtures exhibited the hig indicating high homogeneity. The opposite te] for the H and H-VMA cement content and w/c are believed to be ma

11 B ~(,) '6.E: (i) 40 + al - 80 IH = (1 60 R2= I s) D Cement content =385 kglm3 Á Á Cement content = 500 kglm3 o Homogeneity index (1 H) Fig. 15-Relationship between summation of bleeding and segregation indexes with respect to homogeneity index. 1.0 ACKNOWLEDGMEN The authors wish to acknowledge the financial sui Inc., Cleveland, Ohio, in conducting this research p 5. Japan Society of Civil Engineers, RecommentÚJ REFERENCES 1. Khayat, K. H., "Workability, Testing, and Consolidating Concrete," ACI Materials Joumal, 1999, pp Khayat, K. H.; Assaad, J.; and Daczko, J., Oriented Test Methods to Assess Dynanúc Stabili1 Concrete," ACI Materials Jou17lLll,V. 101, No. 2, Mar. 3. Khayat, K H.; Manai, K; and Trudel, A, "In Si of Wall Elernents Cast Using Self-Consolidating C Joumal, V. 94, No. 6, Nov.-Dec. 1997, pp C 4. Hoshino, M., "Relationship between Bleeding Specirnen Height of Concrete," ACI Materials Jou, Apr. 1989, pp Concrete, T. Ornoto and K Ozawa, oos., JSCE Series 31,1999,77 pp. 6. Van, B. K; Montgornery, D. G.; Hinczak, l.; Testing Methods for Segregation Resistance and