摘要
基于水化-结晶法,以聚乙二醇为相变材料,硫铝酸盐水泥的水化产物为基体,利用聚乙二醇的水溶性和硫铝酸盐水泥的水硬性制备了一种高聚乙二醇含量的水泥基复合相变材料(CPCMs),研究了其微观结构、化学兼容性、晶体结构、相变特性、热稳定性及降温效果.结果表明:聚乙二醇能够均匀地分散在硫铝酸盐水泥水化产物构成的多孔网络结构中,负载情况良好;聚乙二醇与硫铝酸盐水泥水化产物的化学兼容性良好,二者没有发生化学反应;CPCMs在250 ℃以下具有良好的热稳定性,具备用于相变储热沥青路面的温度条件;当聚乙二醇质量分数为36.36%时,CPCMs的相变焓高达62.48 J/g,与对照组硫铝酸盐水泥相比,其表面温度降低了7.3 ℃.
沥青路面在中国应用广泛,然而沥青材料的黑色特性导致其强烈吸收太阳辐
相变储热沥青路面在路面降温领域优势显
近年来,水泥基材料作为用量最大的建筑材料,在相变储热领域的应用愈加广
鉴于此,本文基于水化-结晶法,结合聚乙二醇(PEG)良好的水溶性,以SAC水化产物为基体制备高PEG含量的CPCMs.通过微观试验表征CPCMs的微观组织、化学组成及晶体结构,采用热分析表征其相变特性及热稳定性,最后通过室内照射试验验证其在沥青路面降温领域应用的可行性,以期为制备高相变焓CPCMs和降低沥青路面温度提供依据.
SAC,比表面积为389
SiO2 | CaO | Fe2O3 | Al2O3 | SO3 | MgO | IL |
---|---|---|---|---|---|---|
6.51 | 41.02 | 1.03 | 37.95 | 8.79 | 1.03 | 0.16 |
以1.2作为PEG与水的初始质量比,按照0.2的质量比梯度分别制备5种PEG水溶液,水灰比保持在0.4不变,将PEG溶液缓慢加入水泥中.首先将材料在水泥胶砂搅拌机中低速(140 r/min)搅拌120 s,然后停止搅拌15 s,再高速(280 r/min)搅拌120 s后倒入尺寸为40 mm×40 mm×160 mm的模具中.在(20±1) ℃、相对湿度为95%以上的水泥标准养护条件下养护28 d后,将CPCMs试样从模具中取出并粉碎,分别制得CPCMs碎块和粒径小于0.075 mm的粉体.
需要注意的是,在制备过程中,当PEG与水的质量比超过2.0时,由于PEG含量过高,析出的PEG大量附着在水泥颗粒表面,阻碍了水泥颗粒与自由水的接触,导致水化反应不完全,试样和易性差,无法成型,因此本研究制备的CPCMs中PEG与水质量比最高为2.0.将PEG与水的质量比分别为1.2、1.4、1.6、1.8和2.0的CPCMs分别命名为CPCM1、CPCM2、CPCM3、CPCM4和CPCM5.
使用日本JEOL公司生产的JSM‑IT500LV型扫描电子显微镜(SEM)观察SAC水化产物和CPCMs的形貌与微观结构;使用美国Thermo公司生产的Nicolet iS50型傅里叶变换红外吸收光谱仪(FTIR)来评价PEG和SAC的化学相容性;使用德国Bruker公司生产的D8 Advance型X射线衍射仪(XRD)来表征CPCMs的晶体结构.
CPCMs的热性能包括相变特性和热稳定性.使用美国TA Instruments公司生产的Q10型差示扫描量热仪(DSC)对样品进行测试,升温速率为5 ℃/min,试验温度为20~80 ℃.使用美国TA Instruments公司生产的Q10型热重分析仪(TGA)测试其热稳定性,加热速率为10 ℃/min,测试温度为20~600 ℃.
将尺寸为40 mm×40 mm×160 mm的CPCMs试样标准养护28 d后从模具中取出,每个CPCMS试样用泡沫板包裹保温,将功率为500 W的碘钨灯放置在CPCMs试样上方以模拟太阳辐射,碘钨灯距试样表面高度80 cm,如

图1 室内照射试验示意图
Fig.1 Diagram of indoor irradiation test
Group No. | Sample | |||
---|---|---|---|---|
1 | CPCM1 | CPCM2 | CPCM5 | SAC |
2 | CPCM3 | CPCM4 | CPCM5 | SAC |
3 | CPCM1 | CPCM2 | CPCM3 | CPCM4 |

图2 SAC和CPCMs的SEM图像
Fig.2 SEM images of SAC and CPCMs
(1)SAC中的簇状钙矾石(AFt)晶体和不规则的水化硅酸钙(C‑S‑H)凝胶连接构成了三维网络结构.掺入PEG之后,其微观结构发生了变化,导致单位体积的水化产物含量降低,由此造成水泥水化产物的致密性下降,内部形成了更多的孔隙.微观结构致密性的下降主要是由于水化产物C‑S‑H凝胶的减
(2)随着PEG含量的增加,水化体系中的孔隙逐渐被PEG填充,内部孔隙减少.当PEG与水的质量比达到2.0(即CPCM5)时,水化产物之间的多孔网络结构大部分被PEG填充,形成了牢固的PEG封装体系,表明水泥具有丰富的孔结构,能够作为PEG的载体并且为其提供良好的封装性.
为了评估PEG和SAC水化产物之间可能存在的相互作用,研究二者之间的化学相容性.对SAC和CPCMs样品进行了FTIR分析,结果如

图3 PEG、SAC和CPCMs的FTIR图谱
Fig.3 FTIR spectra of PEG, SAC and CPCMs
Material | Wavenumber/c | Characteristic peak |
---|---|---|
PE | 2 888 | Stretching vibration absorption peak of C—H group |
1 467 | Bending vibration absorption peak of C—H group | |
1 359 | Stretching vibration peak of CH2 group | |
1 342 | Stretching vibration peak of C—H group | |
1 107 | Stretching vibration peak of C—O group | |
962 | Crystallization characteristic peak of PEG | |
843 | Characteristic peak of CH2 group | |
SA | 3 626/3 430 | Stretching vibrational absorption peaks of‑OH groups in ettringite and water molecules |
1 667 |
Bending peak of the‑OH group in Al[(OH)6 | |
1 445 | Vibrational peak of CO group | |
1 112/875 | Asymmetric stretching vibration peaks of SO group and SiO4 group |
由

图4 PEG、SAC和CPCMs的XRD图谱
Fig.4 XRD patterns of PEG, SAC and CPCMs
(1)PEG的XRD图谱中有2个强度很高的特征衍射峰,分别为19.16°和23.26°.
(2)CPCMs的成分除了外掺的PEG之外,主要包括AFt、硫酸钙(CaSO4)、碳酸镁钙(CaMg(CO3)2)、碳酸钙(CaCO3)、钙铝黄长石(C2AS)等水化产物和部分未水化的硫铝酸钙(Ca4Al6SO16),不同PEG含量CPCMs的XRD图谱在对应的位置均显示了衍射峰.表明CPCMs的峰形和衍射角与PEG及SAC的水化产物相似,没有产生新的衍射峰,即PEG与水泥只是物理混合,不参与水泥的水化反应,与FTIR的分析结果一致.
(3)从特征峰强度来看,AFt的衍射峰峰位是9.08°、15.73°和34.91°.对比SAC和CPCMs的XRD图谱发现,随着PEG含量的增加,AFt的衍射峰强度逐渐减小;Ca4Al6SO16的特征峰是23.75°,其强度随着PEG的掺入而增加.这是因为水化过程中析出的PEG晶体覆盖在水泥熟料颗粒的表面,降低了水泥的水化程度,从而导致CPCMs中水化产物AFt的减少以及含有较多未水化的Ca4Al6SO16.

图5 PEG与CPCMs的DSC结果
Fig.5 DSC results of PEG and CPCMs
Sample | w(PEG)/% | Tested enthalpy/ (J· | Theoretical enthalpy/ (J· | Latent heat loss ratio/% | Peak temperature of melting/℃ | Peak temperature of crystallization/℃ |
---|---|---|---|---|---|---|
PEG | 194.98 | 58.73 | 38.06 | |||
CPCM1 | 25.53 | 40.04 | 49.78 | 19.57 | 58.45 | 37.19 |
CPCM2 | 28.57 | 46.14 | 55.71 | 17.18 | 58.30 | 37.32 |
CPCM3 | 31.37 | 54.36 | 61.16 | 11.11 | 58.49 | 38.92 |
CPCM4 | 33.96 | 57.81 | 66.21 | 12.69 | 58.80 | 39.37 |
CPCM5 | 36.36 | 62.48 | 70.89 | 11.86 | 58.67 | 39.74 |
(1) |
式中:HCPCMs为CPCMs的理论相变焓,J/g;w为CPCMs中PEG的质量百分比,%;HPEG为DSC测定的PEG相变焓,J/g.
由
对比
热稳定性是相变材料非常重要的一个性能,决定了相变材料在实际应用中的温度适用范围.

图6 SAC和CPCMs的TG‑DTG曲线
Fig.6 TG‑DTG curves of SAC and CPCMs
(1)SAC的质量损失可以分为2个阶段:第1阶段是AFt在70~140 ℃范围内发生的热分解;第2阶段是C‑S‑H凝胶的脱水,在140~250 ℃范围内发
(2)总的来说,CPCMs的TG和DTG曲线有相同的变化趋势,但相应的质量损失不同.在前2个阶段(70~250 ℃),质量损失与AFt、C‑S‑H凝胶含量有关,且随着PEG含量的增加逐渐减小,SAC和CPCMs的质量损失分别为18.16%、13.88%、10.57%、9.99%、8.72%和7.37%;在300~400 ℃,质量损失与PEG的含量有关,依次增加.这是因为随着 PEG含量的增加,水化生成的AFt和C‑S‑H凝胶含量降低.结果表明,在温度低于250 ℃时,CPCMs的热稳定性高于SAC,且随着PEG含量的增加,CPCMs的热稳定性越来越好,CPCM5在250 ℃以下的质量损失仅有7.37%,而沥青混合料的正常工作温度不高于200 ℃.因此,CPCMs适用于相变储热沥青路面.
为了评估CPCMs的降温能力,在20 ℃室温下对不同PEG掺量的水泥基样品进行照射试验,其表面温度分布如

图7 SAC和CPCMs的表面温度分布
Fig.7 Surface temperature profiles of SAC and CPCMs
(1)聚乙二醇(PEG)在硫铝酸盐水泥(SAC)水化产物的孔隙结构中分散均匀,负载情况良好.PEG没有参与水泥的水化反应,二者只是物理相容,但PEG在一定程度上降低了水泥的水化程度.
(2)PEG的结晶受到限制,导致复合相变材料(CPCMs)的相变焓有不同程度的损失.随着PEG含量的增加,CPCMs的相变焓增大,其中CPCM5的相变焓高达62.48 J/g.此外,CPCMs在250 ℃以下的热稳定性高于SAC,其质量损失在250 ℃以下与PEG的含量呈负相关,其中CPCM5的质量损失低至7.37%,因此CPCMs的工作温度应低于250 ℃.
(3)CPCMs的表面温度均低于SAC的表面温度,且随着PEG含量的增加,其表面温度越来越低,PEG含量最高的CPCM5的表面温度与对照组SAC相比下降了7.3 ℃,表明CPCMs具有良好的降温能力.
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