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      基于響應(yīng)面法的粉煤灰-電石渣基地聚物的砂漿配比優(yōu)化

      2024-09-28 00:00:00王勁松陳瑾但理歐陽高尚杜可杰岳喜祥
      中國粉體技術(shù) 2024年4期
      關(guān)鍵詞:響應(yīng)面法粉煤灰

      摘要:【目的】為改善粉煤灰-電石渣基地聚物砂漿室溫養(yǎng)護下的力學(xué)性能,實現(xiàn)工業(yè)固廢粉煤灰和電石渣的資源再利用?!痉椒ā坷脝我蛩卦囼灤_定電石渣的最優(yōu)摻量,初步確定粉煤灰-電石渣基地聚物砂漿的最優(yōu)取值范圍,然后以NaOH溶液濃度、液固比、水玻璃與NaOH溶液質(zhì)量比為自變量因素,以砂漿28d的抗壓強度和抗折強度為響應(yīng)值,進行響應(yīng)面法實驗,對粉煤灰-電石渣基地聚物砂漿配合比進行優(yōu)化,并進行微觀機制解釋。【結(jié)果】響應(yīng)面法能較為準確地優(yōu)化粉煤灰-電石渣基地聚物砂漿配合比,當粉煤灰和電石渣的質(zhì)量比為7:3、NaOH溶液濃度為10 mol/L、液固比(質(zhì)量比)為0.62、水玻璃與NaOH溶液質(zhì)量比為2.3時,粉煤灰-電石渣基地聚物砂漿綜合性能最優(yōu)?!窘Y(jié)論】在最優(yōu)配比時,粉煤灰-電石渣基地聚物砂漿的水化產(chǎn)物以水合硅酸鈣凝膠、水化硅鋁酸鈣凝膠為主,并隨著固化時間的延長,粉煤灰-電石渣基地聚物體系的微觀結(jié)構(gòu)中凝膠含量增加,表現(xiàn)出更高的致密性以及更好的宏觀力學(xué)性能,粉煤灰-電石渣基地聚物砂漿的綜合力學(xué)性能及施工性能得以提高。

      關(guān)鍵詞:響應(yīng)面法;粉煤灰;電石渣;配比優(yōu)化

      中圖分類號:TU526;TB4文獻標志碼:A

      引用格式:

      王勁松,陳瑾,但理,等.基于響應(yīng)面法的粉煤灰-電石渣基地聚物的砂漿配比優(yōu)化[J].中國粉體技術(shù),2024,30(4):69-80.

      WANG Jinsong,CHENJin,DANLi,etal.Optimization of fly ash-calcium carbide slag-based geopolymer mortar ratio usingresponse surface method[J].China Powder Science and Technology,2024,30(4):69-80.

      地聚物是由具有火山灰活性或潛在膠凝活性的硅鋁酸鹽礦物與堿性激發(fā)劑適當混合而制成。與普通硅酸鹽水泥相比,地聚物具有低能耗、低CO?排放的特點。粉煤灰作為一種常見的地聚物前驅(qū)體材料,主要成分為SiO?和Al?O?,在堿性介質(zhì)的活化下,形成力學(xué)性能與硅酸鹽水泥相當?shù)牟牧?。由于低鈣粉煤灰是一種活性較低的硅鋁基材,在常溫或室溫下制備的粉煤灰基地聚物通常表現(xiàn)出早期強度較低、凝固時間較長、離析層次嚴重等缺點,使其工程應(yīng)用受到較大限制。電石水解得到乙炔氣的副產(chǎn)物電石渣,Ca(OH)?含量較高,近年來被廣泛用于改善粉煤灰基地聚物的砂漿活性I3。Alenyorege等發(fā)現(xiàn)電石渣的摻入可以補充Ca2+,加速聚合反應(yīng)速率,大幅縮短聚合反應(yīng)時間。安強等5通過引入工業(yè)廢棄物電石渣可減少強堿用量,從而提升經(jīng)濟和環(huán)境效益。高英力等6利用響應(yīng)面法對鋼渣、電石渣和脫硫石膏進行地聚物的制備,發(fā)現(xiàn)隨著多元固廢的摻入,能夠生成更多凝膠,使結(jié)構(gòu)更加密實。劉揚等7發(fā)現(xiàn)使用電石渣部分替代粉煤灰制備地聚物,可以大大提高地聚物的力學(xué)強度。綜上,摻入電石渣可有望改善堿激發(fā)粉煤灰地聚物早期水化慢、室溫難以固化等問題,實現(xiàn)廢棄粉煤灰和電石渣的資源再利用,也可有效降低環(huán)境污染等危害。

      近年來,響應(yīng)面法已被廣泛應(yīng)用于砂漿和混凝土的配合比設(shè)計中,取得了顯著的優(yōu)化效果。響應(yīng)面法是一種多因素分析方法,旨在優(yōu)化實驗條件并解決多因素多層次下的持續(xù)響應(yīng)問題。通過建立影響因素與響應(yīng)值之間的函數(shù)關(guān)系,計算各影響因素對應(yīng)的響應(yīng)值,從而為實驗設(shè)計和響應(yīng)預(yù)測提供可靠的數(shù)據(jù)支撐。與傳統(tǒng)的單因子控制變量法和正交實驗法相比,響應(yīng)面法能夠通過建立影響因素與響應(yīng)值的函數(shù)關(guān)系,獲得各因素的最優(yōu)水平,進一步提升實驗效率[8-10]。

      本文中在粉煤灰基地聚物摻入電石渣,并通過單因素試驗確定電石渣的最優(yōu)摻量,然后采用響應(yīng)面曲面法,構(gòu)建多元回歸模型,確定最優(yōu)配比,最后通過微觀分析揭示地聚物水化產(chǎn)物的作用機制,為進一步推進粉煤灰和電石渣在建材資源化利用上提供可靠的數(shù)據(jù)支撐。

      1材料與方法

      1.1試劑材料和儀器設(shè)備

      試劑材料:粉煤灰(河南恒源新材料有限公司);電石渣(鞏義市元亨凈水材料廠)。標準砂(廈門艾思歐標準砂有限公司);水玻璃溶液(Na?O與SiO?的質(zhì)量分數(shù)分別為13.75%和29.99%,浙江嘉興優(yōu)瑞耐材化工有限公司);NaOH溶液(工業(yè)級片狀NaOH與水在一定質(zhì)量比下混合配制而成,河南鄭州鴻騰化工有限公司)。

      粉煤灰和電石渣的物理性質(zhì)如表1所示,粉煤灰和電石渣的物相組成如圖1所示。由圖1和表1可知,粉煤灰的主要成分為石英(SiO?)和莫來石(Al?Si?O??),其中位粒徑d?為8.51 μm,比表面積為422.23 m2/kg;電石渣的主要成分為Ca(OH)?和方解石(CaCO?),其中位粒徑d?o為11.85 μm,比表面積為414.56 m2/kg。

      儀器設(shè)備:NLD-3型水泥膠砂流動度測定儀(世佳試驗儀器廠);TYE-600E型壓力試驗機、TYE-10C型抗折試驗機、JJ-5型行星式水泥膠砂攪拌機(無錫建儀儀器機械有限公司);D/Max2400型X射線衍射儀(XRD,日本理學(xué)株式會社);SDTA851E型綜合熱分析儀(TG-DTG,瑞士梅特勒公司);Nova Nano SEM450型掃描電子顯微鏡(SEM,美國FEI公司)。

      1.2實驗設(shè)計

      1.2.1單因素試驗

      試驗固定膠砂比(質(zhì)量比,下同)為1:3,單因素試驗中電石渣取代率(質(zhì)量分數(shù),下同)為30%,NaOH溶液濃度為10 mol/L,液固比(堿激發(fā)溶液與固體粉煤灰和電石渣粉末之和的質(zhì)量比,下同)為0.64,堿激發(fā)溶液質(zhì)量比(水玻璃溶液與NaOH溶液的質(zhì)量比)為2,作為基本原料用量標準。

      分別研究電石渣取代率(0%、10%、20%、30%、40%)、NaOH溶液濃度(4、6、8、10、12 mol/L)、液固比(0.60、0.62、0.64、0.66、0.68)、堿激發(fā)溶液質(zhì)量比(1、1.5、2、2.5、3)對粉煤灰-電石渣基地聚物砂漿力學(xué)性能的影響,上述參數(shù)選擇均基于以往關(guān)于堿激發(fā)膠凝材料研究成果[13-17]。

      1.2.2響應(yīng)面優(yōu)化設(shè)計

      在單因素試驗的基礎(chǔ)上,以NaOH溶液濃度、液固比、堿激發(fā)溶液質(zhì)量比為自變量因素,以砂漿28 d的抗壓強度和抗折強度為響應(yīng)值,采用響應(yīng)面法中的Box-Behnken模型設(shè)計三因素三水平正交實驗。實驗自變量因素編碼及水平如表2所示,其中液固比是w;,堿激發(fā)溶液質(zhì)量比是w,因素A、B、C分別是NaOH溶液濃度、液固比、堿激發(fā)溶液質(zhì)量比。

      1.3樣品制備與測試

      1.3.1樣品制備

      通過容量瓶定容一定濃度的NaOH溶液,水玻璃與NaOH溶液先后倒入燒杯中,分別按照實驗設(shè)計中的比例配制堿激發(fā)溶液,并在室溫條件下陳化24h。將粉煤灰和電石渣按照實驗設(shè)計中的比例加入到行星式水泥膠砂攪拌機中,邊攪拌邊加入配制好的堿激發(fā)溶液,充分攪拌后置于水泥砂漿三試模具(長、寬、高分別為160、40、40 mm)中,將模具放在振動臺振動成型。室溫靜置1d后脫模,將試件存放于標準養(yǎng)護箱內(nèi),相對濕度≥95%、溫度為(20±2)℃養(yǎng)護。

      1.3.2宏觀性能測試

      1)力學(xué)性能測試

      參照GB/T 17671—2021《水泥膠砂強度檢驗方法(ISO法)》的方法,對養(yǎng)護至設(shè)計齡期的試件進行抗折強度和抗壓強度試驗,其中抗折強度試驗的加載速率為50 N/s,抗壓強度試驗的加載速率為2.4 kN/s。

      2)流動度測試

      按照GB/T 2419—2005《水泥砂漿流動度測定方法》12的方法,對砂漿的流動度進行測定。

      1.3.3微觀性能測試

      1)XRD分析

      測試前先用無水乙醇浸泡樣品使其終止水化,然后再放置在溫度為60℃的烘箱中烘干24 h,接著將樣品磨細,過篩(孔徑為80 μm),最后制樣測試。

      2)TG-DTG分析

      在氮氣作為介質(zhì)的環(huán)境中,溫度為50~1000 ℃,升溫速率為10℃/min。

      3)SEM分析

      在每組試件測試完設(shè)計齡期的抗壓強度后,挑選界面較為平整,且距原試件表面具有一定距離的薄碎片作為所選樣品。

      2結(jié)果與討論

      2.1單因素試驗分析

      圖2所示為各單因素對粉煤灰-電石渣基地聚物砂漿抗壓強度和流動性的影響。由圖2(a)可知,當NaOH溶液濃度過低(如4 mol/L)時,粉煤灰-電石渣基地聚物砂漿的流動性和抗壓強度均較低,這是由于體系中的OH-和Nat濃度較低,不足以有效激發(fā)粉煤灰和電石渣反應(yīng)。當NaOH溶液濃度過高(如12 mol/L)時,粉煤灰-電石渣基地聚物砂漿的流動性和抗壓強度也會下降,這是由于OH-和Na*濃度較高,加大了硅酸鹽和鋁酸鹽礦物在砂漿中的溶解度,從而影響砂漿的均質(zhì)性和結(jié)構(gòu)完整性13,因此,選取NaOH溶液濃度分別為6、8、10 mol/L設(shè)計響應(yīng)面試驗。

      由圖2(b)可知,粉煤灰-電石渣基地聚物砂漿的流動性隨著液固比的增大而逐漸增大,但抗壓強度隨著液固比的增大呈先上升后下降的趨勢,在液固比為0.64時達到最優(yōu)。這是由于適當提高液固比可以改善砂漿的流動性和密實性,減少氣泡和空隙的形成,從而在一定程度上提高強度,而當液固比繼續(xù)增大時,過多的水分導(dǎo)致砂漿中形成更多大尺寸孔隙,使抗壓強度下降14,因此,選取液固比分別為0.62、0.64、0.66設(shè)計響應(yīng)面試驗。

      由圖2(c)可知,粉煤灰-電石渣基地聚物砂漿的流動性隨著堿激發(fā)溶液質(zhì)量比的增大而下降,抗壓強度隨堿激發(fā)溶液質(zhì)量比的增大呈先上升后下降的趨勢。這是由于引入適量水玻璃能促進形成更多的Si—0—Si鍵,從而形成致密的三維網(wǎng)狀結(jié)構(gòu),增強砂漿抗壓強度,而當硅含量過高時,凝固過快導(dǎo)致基質(zhì)結(jié)構(gòu)在早期形成過于緊密,影響強度發(fā)展,因此,選取堿激發(fā)溶液質(zhì)量比分別為1.5、2、2.5設(shè)計響應(yīng)面試驗。

      由圖2(d)可知,隨著電石渣取代率的增加,抗壓強度呈先上升后下降的趨勢,當電石渣摻量增加至40%時,抗壓強度下降且流動性急劇下降,說明電石渣的最佳摻量在30%~40%之間,這一結(jié)果與Suttiprapa等的研究結(jié)果一致16。這是因為當電石渣超過最佳摻量后,會使體系中OH-濃度過高,快速生成的水化產(chǎn)物會在粉煤灰顆粒表面形成一層保護膜,阻礙其繼續(xù)水化,導(dǎo)致強度發(fā)展緩慢[17],因此,綜合力學(xué)性能以及流動性,選擇粉煤灰和電石渣質(zhì)量比為7:3進行其他參數(shù)的優(yōu)化。

      2.2響應(yīng)面優(yōu)化分析

      2.2.1響應(yīng)面試驗結(jié)果

      根據(jù)表2中的設(shè)計條件對粉煤灰-電石渣基地聚物砂漿進行抗壓強度和抗折強度測試,結(jié)果如表3所示。

      2.2.2方差分析

      在響應(yīng)面實驗中,二次多項式模型的系數(shù)和曲線形狀在物理上具有直觀的意義,有助于深入理解試驗結(jié)果背后的規(guī)律,已被廣泛運用于響應(yīng)面模型選擇當中。應(yīng)用統(tǒng)計軟件Design-Export 10對表3中的實驗數(shù)據(jù)進行多元回歸擬合,得到抗壓強度p?、抗折強度p?的預(yù)測函數(shù)如下:

      表4所示為響應(yīng)面模型的方差分析表?;貧w模型中P值通常用于驗證回歸系數(shù)的顯著性,Plt;0.01為非常顯著,0.01≤P≤0.05為顯著,Pgt;0.05為不顯著。在方差分析中F值越大,對應(yīng)的P值就越小,P值越小表明模型越顯著,由表4可知,粉煤灰-電石渣基地聚物砂漿28 d抗壓強度、抗折強度的二次多項式回歸方程P值均lt;0.0001,表明模型與實測值高度吻合,3個單因素對粉煤灰-電石渣基地聚物砂漿強度均有顯著影響,3個因素之間的交互作用對測試結(jié)果也有一定的影響,各因素對粉煤灰-電石渣基地聚物砂漿強度的影響由強到弱的順序為:B、A、C、AB、AC、BC。

      圖3所示為28 d強度預(yù)測值與實際值比較結(jié)果。由圖發(fā)現(xiàn),抗壓強度試驗值均位于預(yù)測直線y=0.977x+0.013附近,抗折強度測試值均位于預(yù)測直線y=0.9776x+0.013附近,說明二次多項式模型提供的預(yù)測響應(yīng)是準確的,可以對粉煤灰-電石渣基地聚物砂漿的抗壓強度、抗折強度進行分析和預(yù)測。

      2.2.3響應(yīng)面分析

      圖4為28d抗壓強度二因素交互作用的三維響應(yīng)面圖。由圖可知,此時第3個因素處于中水平編碼,研究其余2個因素交互作用對粉煤灰-電石渣基地聚物砂漿28d抗壓強度的影響規(guī)律。由圖4(a)可知,當液固比較小時,隨著c(NaOH)增加,抗壓強度呈線性增大的趨勢,當液固比較大時,隨著c(NaOH)增加,抗壓強度變化趨勢不顯著,說明液固比對地聚物砂漿的強度有直接影響,在一定范圍內(nèi),較小的液固比可以提升鋁硅酸鹽的溶解速率,進而提高抗壓強度,當液固比較大時,充分的自由水會占據(jù)孔隙空間,導(dǎo)致試塊的孔隙率偏大,影響試塊強度的發(fā)展。由圖4(b)可知,當c(NaOH)為8~10 mol/L、堿激發(fā)溶液質(zhì)量比為2.1~2.5時,同時增大二者對抗壓強度有顯著提高的作用,說明隨著c(NaOH)增加,體系中的pH提高,粉煤灰玻璃體被大量溶解,同時水玻璃溶液中的[SiO?]?-四面體促進體系中的粉煤灰玻璃體發(fā)生解聚-縮聚反應(yīng),使得體系中凝膠生成量更大。由圖4(c)可知,當液固比為0.62~0.64時,增大堿激發(fā)溶液質(zhì)量比對抗壓強度的提升效果較差;當液固比在0.64~0.66時,增大堿激發(fā)溶液質(zhì)量比對抗壓強度的提升效果較好;因此,c(NaOH)、液固比、堿激發(fā)溶液質(zhì)量比3個因素中,液固比對粉煤灰-電石渣基地聚物砂漿強度的影響最為顯著,且c(NaOH)和液固比的交互作用最為明顯。

      圖5為28 d抗折強度二因素交互作用的3D響應(yīng)面圖。由圖5(a)中可看出,隨著液固比增大,抗折強度呈先增大后降低的趨勢。當液固比較小時,隨著c(NaOH)增加,抗折強度呈先平緩后增大的趨勢,當液固比較大時,隨著c(NaOH)增加,抗折強度先減小后增大。當液固比處在0.62~0.64、c(NaOH)在8~10 mol/L時,抗折強度較高。由圖5(b)中可以看出,隨著堿激發(fā)溶液質(zhì)量比增大,抗折強度呈先增加后平緩的趨勢,隨著c(NaOH)增加,抗折強度呈先緩慢降低后迅速增加的趨勢。由圖5(c)中可以看出,當液固比較小時,隨著堿激發(fā)溶液質(zhì)量比增大,抗折強度呈緩慢增加的趨勢,當液固比較大時,隨著堿激發(fā)溶液質(zhì)量比增大,抗折強度變化趨勢不顯著,因此,在抗折強度二因素交互作用中,與粉煤灰-電石渣基地聚物砂漿28d抗壓強度結(jié)果相同,c(NaOH)與液固比的交互作用最為顯著。

      2.2.4最優(yōu)配合比

      將各響應(yīng)值的最大值作為優(yōu)化目標,采用Design-Expert 10中Numerical模塊對粉煤灰-電石渣基地聚物砂漿配合比進行優(yōu)化,得到的最優(yōu)配合比c(NaOH)為10 mol/L,液固比為0.62,堿激發(fā)溶液質(zhì)量比為2.3。表5為配合比優(yōu)化后預(yù)測值與實際值對比,其中D為預(yù)測值與實測值之間的相對誤差絕對值,計算公式20如下:

      式中:Y為28 d強度的實測值;Yp為28 d強度的預(yù)測值。

      表5所示為配合比優(yōu)化后預(yù)測值與實際值對比。由表可知,抗壓強度、抗折強度預(yù)測值與試驗值之間的相對誤差絕對值D均小于5%,表明該模型精度較高,對粉煤灰-電石渣基地聚物砂漿配合比參數(shù)的優(yōu)化具有一定的參考價值。

      3結(jié)果分析

      3.1微觀物相分析

      3.1.1 XRD分析

      圖6所示為響應(yīng)面實驗確定最優(yōu)配合比下養(yǎng)護7、28 d試件的XRD圖譜。由圖可知,試件在不同齡期的礦物相包含水合硅酸鈣凝膠(calcium silicatehydrated,C-S-H)、水化硅鋁酸鈣凝膠(calciumsilicoaluminatehydrate,C-A-S-H)、CaCO?、Ca(OH)?、石英等。電石渣溶于水后,釋放出OH-和Ca2+,粉煤灰硅鋁玻璃體在OH-侵蝕下開始分解,可溶性SiO?和▲7 dAl?O?與Ca(OH)?反應(yīng)形成C-S-H凝膠和C-A-S-H凝膠。在衍射角20為20°~30°之間出現(xiàn)較寬的駝峰,此處可認為是C-S-H凝膠和C-A-S-H凝膠結(jié)構(gòu)的特520304050601020/)征峰[21]。隨著養(yǎng)護齡期的增長,C-S-H凝膠和C-A-圖6地聚物漿體的XRD譜S-H凝膠的衍射峰增強,Ca(OH)?衍射峰減弱,說明Fig.6 XRD patterns of geopolymer mortar pastes隨著水化反應(yīng)的進行,粉煤灰和電石渣在水化過程中消耗Ca(OH)?,形成了更多的C-S-H凝膠和C-A-S-H凝膠,二者都有石英相的尖峰,說明凝膠體系中仍有未反應(yīng)的石英。此外,檢測中出現(xiàn)CaCO?的衍射峰,表明凝膠體系中部分Ca(OH)?與空氣中的CO?反應(yīng)生成CaCO?,一定量的CaCO?有助于填充基體孔隙,利于強度的發(fā)展。

      3.1.2 TG-DTG分析

      為了進一步分析復(fù)合凝膠材料水化產(chǎn)物的組成,對響應(yīng)面試驗確定最優(yōu)配合比下的試件進行熱重分析,結(jié)果如圖7所示。圖中出現(xiàn)3個主要的失質(zhì)量峰,在溫度為50~200 ℃時出現(xiàn)的失質(zhì)量峰歸因于C-S-H凝膠、C-A-S-H凝膠脫水,隨著養(yǎng)護齡期的增加,粉煤灰-電石渣地聚物的失質(zhì)量峰逐漸增加,失質(zhì)量率由4.85%變?yōu)?.22%,表明隨著養(yǎng)護齡期的增加,膠凝體系中形成了更多的C-S-H凝膠、C-A-S-H凝膠,這是力學(xué)強度增加的主要原因[23-24]。在溫度為400~500 ℃處,試件在7d時,有Ca(OH)?脫水形成的明顯放熱峰,失質(zhì)量率為1.16%,而隨著養(yǎng)護齡期的增加,28 d時粉煤灰-電石渣地聚物的失質(zhì)量率變?yōu)?.81%,僅能觀察到Ca(OH)?脫水形成較弱的放熱峰,表明Ca(OH)?在水化過程中不斷參與反應(yīng)生成了新的水化產(chǎn)物,這與XRD中發(fā)現(xiàn)的結(jié)果一致。此外,在溫度為600~700℃處出現(xiàn)的失質(zhì)量峰是由CaCO?的分解引起的,隨著養(yǎng)護齡期的增加,CaCO?峰值逐漸減弱,失質(zhì)量率由7d時的3.93%變?yōu)?8d時的1.66%,這是由于早期水化程度低,有較多的Ca(OH)?發(fā)生了碳化,隨著養(yǎng)護齡期的增加,更多的Ca(OH)?參與反應(yīng),僅有少量的Ca(OH)?發(fā)生了碳化,使膠凝體系中的CaCO?含量降低(25。

      3.2微觀結(jié)構(gòu)分析

      圖8所示為響應(yīng)面實驗確定最優(yōu)配合比下的養(yǎng)護7 、28d試件的SEM圖像。由圖可知,在養(yǎng)護齡期為7d時,凝膠體系中粉煤灰反應(yīng)不完全,在粉煤灰-電石渣地聚物基體中形成了分布不均勻的空洞,而隨著養(yǎng)護齡期的增加,粉煤灰顆粒部分表面被NaOH溶液溶解,凝膠顆粒交聯(lián)融合形成致密的網(wǎng)狀結(jié)構(gòu)。在齡期為28d時,凝膠體系中的粉煤灰玻璃微珠幾乎完全被絮狀凝膠包裹,只有少數(shù)玻璃微珠處于部分裸露狀態(tài),使凝膠結(jié)構(gòu)更加致密,有利于強度的進一步提升。

      4結(jié)論

      1)根據(jù)單因素設(shè)計試驗,通過分析電石渣取代率對粉煤灰-電石渣基地聚物砂漿抗壓強度和流動性的影響,得出粉煤灰、電石渣前驅(qū)體的最優(yōu)配合比為7:3。

      2)根據(jù)響應(yīng)面法設(shè)計實驗,通過構(gòu)建粉煤灰-電石渣基地聚物砂漿28d的抗壓強度和抗折強度的二次多項式回歸模型,得出最佳配合比參數(shù)c(NaOH)為10 mol/L,液固比為0.62,水玻璃與c(NaOH)質(zhì)量比為2.3,在此條件下,28 d的抗壓強度為33.24 MPa,28d的抗折強度為4.65 MPa,為粉煤灰-電石渣基地聚物砂漿的配合比設(shè)計提供參考。

      3)根據(jù)微觀分析試驗,通過XRD、TG-DTG、SEM分析可知,在最優(yōu)配比時,粉煤灰-電石渣基地聚物砂漿的水化產(chǎn)物以C-S-H凝膠、C-A-S-H凝膠為主,隨著固化時間的延長,該地聚物體系的微觀結(jié)構(gòu)中凝膠含量增加,表現(xiàn)出更高的致密性以及更好的宏觀力學(xué)性能,粉煤灰-電石渣地聚物砂漿的綜合力學(xué)性能及施工性能得以提高。

      利益沖突聲明(Conflict of Interests)

      所有作者聲明不存在利益沖突。

      All authors disclose no relevant conflict of interests.

      作者貢獻(Authors'Contributions)

      王勁松、陳瑾、但理、岳喜祥進行了實驗設(shè)計,王勁松、陳瑾、歐陽高尚、杜可杰參與了論文的寫作和修改。所有作者均閱讀并同意了最終稿件的提交。

      The study was designed by WANG Jinsong,CHENJin,DANLi,and YUE Xixiang.The manuscript waswritten and revised by WANG Jinsong,CHENJin,OUYANGGaoshang,and DU Kejie.All authors have readthe last version of the paper and consented to its submission.

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      Optimization of fly ash-calcium carbide slag-based geopolymermortar ratio using response surface method

      WANG Jinsong14,CHEN Jin1?,DAN Lila,OUYANG Gaoshang2,DU Kejie,YUE Xixiang1ala.School of Civil Engineering,1b.Schoo of Chemistry and Chemical Engineering,University of South China,Hengyang 421001,China;

      2.School of Materials Science and Engineering,Wuhan University of Technology,Wuhan 430070,China

      Abstract

      Objective Fly ash-based geopolymers prepared at room temperature usually exhibit disadvantages such as low early strength,longsetingtime,and high segregation levels.The study aims to improve the mechanical properties of fly ash-calcium carbideslag-based geopolymer mortar maintained at room temperature,promoting the reuse of industrial solid wastes such as fly ash andcalcium carbide slag.

      Methods Using the one-factor tests,the study initially fixed the binder-to-sand ratio at 1:3(mass ratio;the following ratios arethe same);the calcium carbide slag replacement rate at 30%;sodium hydroxide solution concentration at 10 mol/L;liquid-to-solid ratio(mass ratio of alkali activation solution to the sum of the fly ash and calcium carbide slag powder)at 0.64;and themass ratio of alkali activation solution(mass ratio of water-glass solution to sodium hydroxide solution)at 2.These served as thebasic material parameters.The study respectively investigated the effects of different calcium carbide slag replacement rates(0%,10%,20%,30%,40%),NaOH solution concentrations(4,6,8,10,12 mol/L),liquid-solid ratios(0.60,0.62,0.64,0.66,0.68),mass ratios of alkali activation solution(1,1.5,2,2.5,3)on the mechanical properties of the geopoly-mermortar.Then,based on the one-factor tests,the Box-BehnKen model in response surface methodology was used to design athree-factor,three-level test with NaOH solution concentration,liquid-solid ratio,and alkali activation solution mass ratio asindependentvariables.The compressive and flexural strength of the mortar at 28 days were taken as response values.

      Results and Discussion Fig.1 showed the effects of calcium carbide slag substitution rate on the compressive strength and fluid-ity of fly ash-based geopolymer at 28 days.With the increase in the replacement rate of calcium carbide slag,thecompressivestrengthinitilly increased and then decreased.When the dosage of calcium carbide slag increased to 40%,the compressivestrength decreased and the fluidity decreased sharply,indicating that the optimal dosage of calcium carbide slag was 30%.Fig.2 showed the comparison between the predicted and actual values after the response surface optimization design,and it wasfound that all the points were located near the straight line y=x.The verification test of the optimal mix ratio was carried out,asshown in Tab.6,and it was found that the absolute value of the relative error was less than 5%.This indicated that the modelhas high accuracy and provides a valuable reference for the optimization of fy ash-calcium carbide slag mortar proportion param-eters.The effects of the interaction of the two factors on the mechanical properties were shown in Figs.3 and 4,indicating thatthe interaction of c(NaOH)and liquid-solid ratio was most significant for both 28-day compressive strength and flexural strengthof fly ash-calcium carbide slag-based mortar.Figs.5,6,and 7 showed the mechanistic analysis of the specimens under the opti-mal mix ratio determined by response surface tests.During the hydration reaction,fly ash and calcium carbide slag consumedCa(OH)?and formed more C-(A)-S-H gels.SEM images of specimens maintained for 7 and 28 days under the optimal mix ratioand determined by response surface tests were shown in Fig.8.From the figure,it was found that at 7 days,the reaction of flyash in the gel system was incomplete,and unevenly distributed voids were formed in the fly ash-calcium carbide slag geopolymermatrix.As maintenance period increased,parts of the surface of the fly ash particles were dissolved by the NaOH solution,andthe gel particles were crosslinked and fused to form a dense mesh structure.SEM images showed that at 28 days,the fly ashglass particles in the gel system were almost completely wrapped by the flocculent gel,with only a few glass particles partiallyexposed.This resulted in a denser gel structure,which was conducive to its further enhancement in strength.

      Conclusion In the paper,the optimal mix ratio of fly ash and calcium carbide slag precursor was initially determined throughone-way design tests.Then,by analyzing the effects of varying calcium carbide slag substitution rates on the compressivestrength and fluidity of the fly ash-calcium carbide slag-based geopolymer mortar,the optimal mix ratio was 7:3.Then,utiliz-ing the response surface methodology,a quadratic polynomial regression model was constructed to predict the compressive andflexural strength of the fly ash-calcium carbide slag-based geopolymer mortar at 28 days.The following optimal parameters wereidentified:ac(NaOH)concentration of 10 mol/L,a liquid-solid ratio of 0.62,and a mass ratio of water glass to c(NaOH)of 2.3.With those parameters,the compressive strength at 28 days was 33.24 MPa and the flexural strength at 28 days was4.65 MPa,providing a reference to the proportional design of the fly ash-calcium carbide slag-based geopolymer mortar.Finally,microanalysistests,including XRD,TG-DTG,and SEM analysis,showed that the hydration products of the geopoly-mer mortar were dominated by C-S-H and C-A-S-H gels at the optimal proportion.With the extension of the curing time,thegel content in the microstructure increased,which exhibited higher densification as well as improved macroscopic mechanicalproperties.The comprehensive mechanical properties and construction performance of fly ash-calcium carbide slag geopolymermortar were improved.

      Keywords:response surface method;flyash;calcium carbide slag;optimal proportioning

      (責(zé)任編輯:孫媛媛)

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