自20 世紀80 年代，外加劑，主要是高效減水劑，在(zai)國內的(de)混(hun)凝(ning)土(tu)(tu)市(shi)場逐步推廣應用(yong)，尤(you)其是(shi)在(zai)高強混(hun)凝(ning)土(tu)(tu)和泵送混(hun)凝(ning)土(tu)(tu)中(zhong)，已成為(wei)不可或缺(que)的(de)組分(fen)。多年來混(hun)凝(ning)土(tu)(tu)技術只(zhi)有少數(shu)幾次(ci)(ci)重(zhong)要(yao)的(de)突破(po)，40 年代開(kai)發的(de)引氣作用(yong)是(shi)其中(zhong)之一(yi)，它改(gai)變了北美混(hun)凝(ning)土(tu)(tu)技術的(de)面貌(mao); 高效減水(shui)(shui)劑(ji)是(shi)另一(yi)次(ci)(ci)重(zhong)大(da)突破(po)，它在(zai)今后許多年里將(jiang)對混(hun)凝(ning)土(tu)(tu)的(de)生產(chan)與應用(yong)帶來巨大(da)影響。對于高效減水(shui)(shui)劑(ji)，行(xing)業部分(fen)從業者(zhe)誤將(jiang)它作為(wei)萬靈藥。東(dong)方雨虹外(wai)加劑(ji)自覺有義務為(wei)此(ci)誤區(qu)進行(xing)客觀的(de)分(fen)析與科普，借用(yong)覃維祖學者(zhe)的(de)文章(zhang)，就這一(yi)問題(ti)進行(xing)分(fen)析。東(dong)方雨虹外(wai)加劑(ji)事業部|官方網站(zhan) |混(hun)凝(ning)土(tu)(tu)外(wai)加劑(ji)_聚羧酸母液_砂漿(jiang)外(wai)加劑(ji)

　　任何事物(wu)都有其(qi)兩面(mian)性，人們常(chang)常(chang)在重視其(qi)作用的同時，卻容(rong)易忽(hu)略了另一面(mian)，包(bao)括可能出現的負面(mian)作用、應(ying)用上的局限性等(deng)。本(ben)文就這一問題談談看法，僅是拋磚引玉，希(xi)望引起同行(xing)的關注。

　　1 . 適用范圍(wei)

　　高效減(jian)(jian)(jian)水(shui)(shui)劑在(zai)一些國家(jia)更(geng)多(duo)稱呼為(wei)(wei)超塑化劑，顧名思義，它(ta)非(fei)常適用(yong)于(yu)制(zhi)備超塑化混(hun)凝土(tu)拌(ban)(ban)合(he)(he)物。當然，它(ta)最適用(yong)于(yu)拌(ban)(ban)制(zhi)流(liu)(liu)動(dong)度大(da)、漿(jiang)(jiang)體(ti)(ti)(ti)量(liang)多(duo)、水(shui)(shui)膠(jiao)比低的(de)(de)拌(ban)(ban)合(he)(he)物，即(ji)泵送高強混(hun)凝土(tu)。但對于(yu)另一些混(hun)凝土(tu)，例如水(shui)(shui)工(gong)(gong)(gong)大(da)壩施工(gong)(gong)(gong)澆筑的(de)(de)混(hun)凝土(tu)，其骨料最大(da)粒徑大(da)( 可(ke)達150mm) 、漿(jiang)(jiang)體(ti)(ti)(ti)量(liang)較(jiao)少(shao)且流(liu)(liu)動(dong)度不(bu)大(da)，需要(yao)通(tong)過采用(yong)強力(li)(li)振搗或振動(dong)碾壓作用(yong)使其密實(shi)成型的(de)(de)混(hun)凝土(tu)，高效減(jian)(jian)(jian)水(shui)(shui)劑就未(wei)必適用(yong)了。出(chu)于(yu)保持水(shui)(shui)膠(jiao)比不(bu)變，以(yi)滿足(zu)結構(gou)設計(ji)要(yao)求(qiu)的(de)(de)力(li)(li)學性能(neng)參數為(wei)(wei)前提(ti)，減(jian)(jian)(jian)少(shao)用(yong)水(shui)(shui)量(liang)，可(ke)以(yi)同時減(jian)(jian)(jian)少(shao)膠(jiao)結材料為(wei)(wei)思路，國內許(xu)多(duo)水(shui)(shui)工(gong)(gong)(gong)大(da)壩施工(gong)(gong)(gong)中也(ye)都在(zai)摻用(yong)高效減(jian)(jian)(jian)水(shui)(shui)劑。實(shi)際上(shang)，這樣的(de)(de)應(ying)用(yong)是(shi)有問題的(de)(de)，因為(wei)(wei)早先水(shui)(shui)工(gong)(gong)(gong)混(hun)凝土(tu)里(li)摻用(yong)的(de)(de)是(shi)引(yin)氣劑或木質素(su)類的(de)(de)普通(tong)型減(jian)(jian)(jian)水(shui)(shui)劑，它(ta)們的(de)(de)減(jian)(jian)(jian)水(shui)(shui)率小，而且由于(yu)有引(yin)氣作用(yong)，增加了漿(jiang)(jiang)體(ti)(ti)(ti)量(liang)，所以(yi)當用(yong)水(shui)(shui)量(liang)與膠(jiao)結材料用(yong)量(liang)同時減(jian)(jian)(jian)少(shao)，也(ye)就是(shi)漿(jiang)(jiang)體(ti)(ti)(ti)量(liang)減(jian)(jian)(jian)少(shao)時，可(ke)以(yi)維持大(da)致平(ping)衡，保證(zheng)有足(zu)夠的(de)(de)填充骨料空隙、包裹骨料并提(ti)供和易性的(de)(de)漿(jiang)(jiang)體(ti)(ti)(ti)，這是(shi)拌(ban)(ban)合(he)(he)物在(zai)澆筑后能(neng)夠密實(shi)成型的(de)(de)必要(yao)條件(jian)。

　　反之(zhi)，在(zai)現(xian)(xian)今摻用(yong)(yong)高效減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)劑(ji)(ji)的(de)(de)(de)拌(ban)合(he)物(wu)(wu)里，由(you)于其(qi)減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)率(lv)(lv)很大，用(yong)(yong)水(shui)(shui)(shui)量(liang)(liang)可以大幅度(du)減(jian)(jian)(jian)(jian)(jian)小，若膠(jiao)結(jie)材料(liao)(liao)用(yong)(yong)量(liang)(liang)也同時(shi)(shi)減(jian)(jian)(jian)(jian)(jian)少，總(zong)漿(jiang)體(ti)(ti)量(liang)(liang)則(ze)明(ming)(ming)(ming)顯減(jian)(jian)(jian)(jian)(jian)少。固(gu)然，由(you)于高效減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)劑(ji)(ji)對于水(shui)(shui)(shui)泥強烈的(de)(de)(de)分(fen)(fen)散作(zuo)用(yong)(yong)，使得(de)(de)(de)原有水(shui)(shui)(shui)泥膠(jiao)團所束縛的(de)(de)(de)自由(you)水(shui)(shui)(shui)得(de)(de)(de)到釋放，這使得(de)(de)(de)漿(jiang)體(ti)(ti)可以在(zai)拌(ban)合(he)物(wu)(wu)中更均勻地分(fen)(fen)布，換句話(hua)說，具備合(he)適(shi)工作(zuo)度(du)拌(ban)合(he)物(wu)(wu)所需要的(de)(de)(de)漿(jiang)體(ti)(ti)量(liang)(liang)在(zai)減(jian)(jian)(jian)(jian)(jian)小。但(dan)是(shi)在(zai)某(mou)些時(shi)(shi)候，上述的(de)(de)(de)平衡(heng)被打破，出(chu)現(xian)(xian)漿(jiang)體(ti)(ti)量(liang)(liang)明(ming)(ming)(ming)顯不(bu)足的(de)(de)(de)現(xian)(xian)象，澆筑時(shi)(shi)出(chu)現(xian)(xian)嚴重的(de)(de)(de)分(fen)(fen)層離析，大顆粒骨(gu)料(liao)(liao)浮在(zai)表面，硬化后骨(gu)料(liao)(liao)周邊呈(cheng)現(xian)(xian)漿(jiang)體(ti)(ti)明(ming)(ming)(ming)顯不(bu)足。這種現(xian)(xian)象筆者曾在(zai)一(yi)水(shui)(shui)(shui)電站工地比(bi)較兩(liang)種減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)率(lv)(lv)不(bu)同的(de)(de)(de)高效減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)劑(ji)(ji)時(shi)(shi)，所澆筑的(de)(de)(de)混(hun)凝土塊(kuai)體(ti)(ti)上見到。使用(yong)(yong)減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)率(lv)(lv)更高，因此用(yong)(yong)水(shui)(shui)(shui)量(liang)(liang)與膠(jiao)結(jie)材料(liao)(liao)用(yong)(yong)量(liang)(liang)更少的(de)(de)(de)拌(ban)合(he)物(wu)(wu)所澆筑的(de)(de)(de)塊(kuai)體(ti)(ti)，骨(gu)料(liao)(liao)周邊呈(cheng)現(xian)(xian)漿(jiang)體(ti)(ti)明(ming)(ming)(ming)顯不(bu)足的(de)(de)(de)現(xian)(xian)象; 而摻用(yong)(yong)減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)率(lv)(lv)較小的(de)(de)(de)減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)劑(ji)(ji)澆筑的(de)(de)(de)塊(kuai)體(ti)(ti)，骨(gu)料(liao)(liao)周邊就(jiu)(jiu)沒有漿(jiang)體(ti)(ti)不(bu)足的(de)(de)(de)現(xian)(xian)象; 且用(yong)(yong)前一(yi)種減(jian)(jian)(jian)(jian)(jian)水(shui)(shui)(shui)劑(ji)(ji)，但(dan)摻量(liang)(liang)適(shi)當(dang)減(jian)(jian)(jian)(jian)(jian)小時(shi)(shi)，拌(ban)合(he)物(wu)(wu)出(chu)現(xian)(xian)離析的(de)(de)(de)現(xian)(xian)象也就(jiu)(jiu)得(de)(de)(de)到明(ming)(ming)(ming)顯改善。

       水(shui)(shui)工(gong)(gong)大壩施工(gong)(gong)澆筑的(de)混凝(ning)土(tu)中，摻(chan)用廉價得(de)(de)多、摻(chan)量也小得(de)(de)多的(de)普(pu)通(tong)引氣型減(jian)水(shui)(shui)劑(ji)，要(yao)比(bi)使(shi)(shi)用高(gao)效減(jian)水(shui)(shui)劑(ji)經濟(ji)性更(geng)好(hao)、使(shi)(shi)用效果更(geng)佳。事實上，國外的(de)水(shui)(shui)工(gong)(gong)大壩施工(gong)(gong)澆筑的(de)混凝(ning)土(tu)，可能使(shi)(shi)用高(gao)效減(jian)水(shui)(shui)劑(ji)的(de)例子，即使(shi)(shi)有也不會多見，當然不包括那種采用預填骨(gu)料后再壓漿或(huo)細石混凝(ning)土(tu)的(de)特殊施工(gong)(gong)工(gong)(gong)藝(yi)。

　　再有，在(zai)澆筑混(hun)凝(ning)(ning)土路面板(ban)(ban)(ban)(ban)或橋面板(ban)(ban)(ban)(ban)時(shi)，通常(chang)所用(yong)拌(ban)(ban)合(he)物的工(gong)作(zuo)(zuo)度(du)一般不(bu)大，坍落度(du)控(kong)制在(zai)30~50mm，使(shi)用(yong)高(gao)效減水劑(ji)的效果就(jiu)會大打折(zhe)扣。特別(bie)是在(zai)采用(yong)滑模攤(tan)鋪(pu)工(gong)藝(yi)鋪(pu)筑路面板(ban)(ban)(ban)(ban)時(shi)，因(yin)為(wei)(wei)由攤(tan)鋪(pu)機所帶的模板(ban)(ban)(ban)(ban)在(zai)2 ～ 3min 或稍長一點的時(shi)間就(jiu)會滑離，因(yin)此需(xu)要拌(ban)(ban)合(he)物在(zai)振搗(dao)棒(bang)的振實作(zuo)(zuo)用(yong)一旦(dan)消失，即(ji)攤(tan)鋪(pu)機向前行進時(shi)，就(jiu)迅(xun)速(su)恢復(fu)原(yuan)來的黏稠狀態( 材(cai)料學上稱之為(wei)(wei)“觸變性良好”) ，而(er)(er)不(bu)會在(zai)模板(ban)(ban)(ban)(ban)滑離時(shi)出現所謂“塌邊”現象。顯然(ran)，滿足(zu)這種施工(gong)工(gong)藝(yi)需(xu)要的拌(ban)(ban)合(he)物不(bu)適合(he)摻(chan)用(yong)高(gao)效減水劑(ji)，特別(bie)是用(yong)于預拌(ban)(ban)混(hun)凝(ning)(ning)土“保坍性”好的品種更(geng)不(bu)適用(yong)。此外，用(yong)高(gao)效減水劑(ji)降(jiang)低水膠比的拌(ban)(ban)合(he)物硬(ying)化后抗壓強度(du)可以大幅度(du)提高(gao)，然(ran)而(er)(er)抗折(zhe)強度(du)增長幅度(du)通常(chang)相對較小，而(er)(er)且(qie)開(kai)裂敏感(gan)性還會增大，因(yin)此總體來說，混(hun)凝(ning)(ning)土路面板(ban)(ban)(ban)(ban)或橋面板(ban)(ban)(ban)(ban)施工(gong)要慎用(yong)高(gao)效減水劑(ji)。

　　其實，在(zai)配制工(gong)民(min)建(jian)和土木工(gong)程中用(yong)量(liang)最(zui)大(da)的C30( 應該占到總(zong)量(liang)的1 /2 以上(shang)) 或(huo)(huo)更低(di)一(yi)些(xie)強度(du)等級的泵(beng)(beng)送混(hun)凝(ning)土時，高(gao)效減水劑也并非一(yi)定適用(yong)，或(huo)(huo)者說并非是一(yi)個必不(bu)可少的組(zu)分。盡(jin)管泵(beng)(beng)送工(gong)藝需要拌(ban)(ban)合(he)物的流動性好，然而在(zai)高(gao)效減水劑應用(yong)之前很(hen)久，泵(beng)(beng)送工(gong)藝就已經(jing)在(zai)國(guo)內(nei)(nei)外(wai)混(hun)凝(ning)土澆筑過(guo)程中應用(yong)開來，例如上(shang)海寶鋼建(jian)設時就采用(yong)木質磺酸鹽類(lei)(lei)引(yin)氣減水劑進(jin)行泵(beng)(beng)送，效果很(hen)好。而另一(yi)方面，由于配制這(zhe)類(lei)(lei)拌(ban)(ban)合(he)物所用(yong)膠(jiao)結(jie)(jie)材(cai)料(liao)(liao)(liao)用(yong)量(liang)一(yi)般不(bu)很(hen)大(da)，所以當水膠(jiao)比(bi)大(da)幅度(du)降低(di)時，如上(shang)所述(shu)，若要保持漿體量(liang)的大(da)致平衡，就需要增加膠(jiao)結(jie)(jie)材(cai)料(liao)(liao)(liao)的用(yong)量(liang)，而這(zhe)不(bu)僅(jin)不(bu)經(jing)濟，還會因膠(jiao)結(jie)(jie)材(cai)料(liao)(liao)(liao)水化(hua)溫升(sheng)的增大(da)引(yin)起(qi)開裂(lie)敏感性的提高(gao)，這(zhe)也是為(wei)什么國(guo)內(nei)(nei)這(zhe)種強度(du)等級或(huo)(huo)更低(di)一(yi)點的混(hun)凝(ning)土中，膠(jiao)結(jie)(jie)材(cai)料(liao)(liao)(liao)始(shi)終居高(gao)不(bu)下(xia)的重要原(yuan)因。