摘要
采用破碎、碳化和腐熟3种方法预处理园林垃圾,并按质量分数0%、3%、6%、9%和12%掺入工程弃土中,制备得到工程弃土烧结砖,并对其进行基本性能研究.结果表明:掺入园林垃圾后混合物料的塑限和液限提高,烧结后的主要产物为钾长石、斜长石、赤铁矿和莫来石;烧结砖的孔隙率增加、微观结构变得松散、吸水率增大、表观密度降低、体积收缩先增大后减小、质量损失增大;碳化园林垃圾因其颗粒小、有机质含量少、对烧结砖微观结构影响小且烧结产物中含有莫来石等,对烧结砖的力学性能影响最小;以质量分数6%的碳化园林垃圾掺入工程弃土中所制备的烧结砖抗压强度有所提升.
目前中国每年产生的工程弃土超过30亿
园林垃圾的主要成分是木质素和纤维
园林垃圾(GW)来自于某园林采集的落叶和枯枝,其中落叶包括女贞树叶、桐树叶、香樟树叶和柳树叶等.采用破碎、碳化和腐熟3种方式对其进行预处理,分别得到破碎园林垃圾(PGW)、碳化园林垃圾(CGW)和腐熟园林垃圾(DGW).其中,破碎垃圾过筛后粒径小于1.0 mm;碳化使用250 mm×250 mm×100 mm的带盖方形坩埚进行,在电炉中先以5 ℃/min的速率升温至270 ℃且保温2 h,再以相同速率继续升温至570 ℃且保温2 h,然后自然冷却;腐熟使用腐熟专菌种,在密封罐中进行,环境温度为(20±2) ℃,保持原料潮湿,全程持续3个月,期间每隔7 d取出原料,翻动搅拌并补充水分.
CS和3种预处理GW的外观如

图1 CS与3种预处理GW的外观
Fig.1 Appearance of construction spoil and three kinds of treated garden waste
Type | Cellulose | Hemicellulose | Lignin |
---|---|---|---|
PGW | 0.56 | 2.35 | 0.83 |
CGW | 2.99 | 8.85 | 28.78 |
DGW | 11.75 | 11.70 | 14.27 |
Material | Si | Al | Ca | Fe | K | Na | Mg | Ti | Other |
---|---|---|---|---|---|---|---|---|---|
CS | 55.08 | 11.18 | 10.21 | 11.49 | 6.17 | 1.65 | 1.97 | 1.33 | 0.92 |
GW | 33.91 | 7.36 | 33.30 | 9.10 | 5.83 | 1.09 | 2.98 | 0.95 | 5.48 |

图2 CS与GS的颗粒级配曲线
Fig.2 Particle gradation curves of construction spoil and garden waste

图3 CS的矿物组成
Fig.3 Mineral composition of construction spoil
由
由
由
由
以CS质量为基准,将3种GW按照质量分数0%、3%、6%、9%和12%分别掺入CS中,制备得到园林垃圾-工程弃土烧结砖(GW‑SCSB).GW‑SCSB 试件的编号和配方如
Specimen No. | w(PGW)/% | Moisture content(by mass)/% | Specimen No. | w(CGW)/% | Moisture content(by mass)/% | Specimen No. | w(DGW)/% | Moisture content(by mass)/% |
---|---|---|---|---|---|---|---|---|
GW0‑SCSB | 0 | 25.3 | GW0‑SCSB | 0 | 25.3 | GW0‑SCSB | 0 | 25.3 |
PGW3‑SCSB | 3 | 21.3 | CGW3‑SCSB | 3 | 24.0 | DGW3‑SCSB | 3 | 26.9 |
PGW6‑SCSB | 6 | 24.2 | CGW6‑SCSB | 6 | 26.7 | DGW6‑SCSB | 6 | 27.6 |
PGW9‑SCSB | 9 | 25.3 | CGW9‑SCSB | 9 | 28.8 | DGW9‑SCSB | 9 | 28.4 |
PGW12‑SCSB | 12 | 26.2 | CGW12‑SCSB | 12 | 29.5 | DGW12‑SCSB | 12 | 29.9 |

图4 GW‑SCSB的制备流程
Fig.4 Preparation process of GW‑SCSB
首先将加水后的混合物料在30~40 ℃的密封条件下陈化3 d,使其可塑性进一步提高;然后将其放入普通小型擀面机中挤压成1 mm厚的泥土薄片,糅合并再次挤压,反复5次完成练泥过程;接着采用真空挤出机将该泥土薄片在-80~-90 kPa的真空环境下缓慢挤成泥条;再将泥条切割为等长泥块,放入电子干燥箱中进行干燥,干燥分2个阶段——先在40 ℃下慢速干燥12 h,再在100~105 ℃下快速干燥8 h;最后取出干燥泥块放入电子窑炉中进行烧结,以200 ℃/h的速率升温至900 ℃,并在900 ℃下保温8 h,自然冷却得到GW‑SCSB试件.
依据JTG E40—2007《公路土工试验规程》,采用LP‑100D型液塑限联合测定仪测试混合物料的界限含水率(塑限(wp)、液限(wl))和塑性指数(Ip).
依据GB/T 2542—2012《砌墙砖试验方法》进行GW‑SCSB的物理力学性能试验,包括烧结砖的24 h吸水率(W24)、煮沸3 h吸水率(W3)、饱和系数(K)、表观密度(ρ)、体积收缩(S)、质量损失(W)、抗压强度和抗折强度等.

图5 混合物料的界限含水率、塑性指数
Fig.5 Limit moisture content and plasticity index of mixed materials

图6 GW‑SCSB的物理性能试验结果
Fig.6 Physical performance test results of GW‑SCSB
GW‑SCSB是一种可用于砌体结构的建筑材料,因此抗压强度是最重要的评价指标之一.

图7 GW‑SCSB的抗压强度和抗折强度曲线
Fig.7 Compressive strength and flexural strength curves of GW‑SCSB
不同于抗压强度,GW‑SCSB抗折强度的变化趋势较为简单.由

图8 未掺GW和掺12%GW烧结砖的XRD图谱
Fig.8 XRD patterns of SCSB without and with 12% GW
Specimen No. | Quartz | Potassium feldspar | Plagioclase | Calcite | Dolomite | Hematite | Ankerite | Clay | Mullite |
---|---|---|---|---|---|---|---|---|---|
CS | 48.3 | 3.2 | 22.5 | 4.4 | 0.4 | 0.8 | 0 | 19.7 | 0 |
GW0‑SCSB | 40.9 | 17.8 | 28.7 | 3.7 | 0 | 7.4 | 1.5 | 0 | 0 |
PGW12‑SCSB | 47.1 | 21.0 | 25.8 | 0 | 0.8 | 5.1 | 0.2 | 0 | 0 |
CGW12‑SCSB | 44.1 | 21.5 | 27.1 | 0 | 0 | 2.5 | 1.6 | 1.0 | 2.2 |
DGW12‑SCSB | 41.4 | 16.9 | 28.2 | 0.7 | 0 | 3.4 | 2.7 | 0.5 | 6.2 |
对比PGW、CGW和DGW的掺入对SCSB产物的影响,发现主要区别在于莫来石矿物相的产生,掺入DGW后,烧结产生了最多的莫来石;同时石英含量最低,钾长石含量最低,与不掺GW时的矿物含量最接近,这可能是部分黏土受到了某种催化作用.GW中含有大量钙,而3种GW‑SCSB较SCSB中的方解石含量均大幅降低,这是由于方解石在高温下分解产生氧化钙和二氧化碳,钙是一种有效的助熔剂,可以降低弃土中矿物的熔点,从而促进部分化学反应的进行.
对比掺入PGW和CGW后的产物结果,可以看到石英含量和钾长石含量均较不掺时更高,说明破碎和碳化更有助于钾长石的生成.考虑到制砖试验和XRD检测中可能存在的误差,不同处理后的GW对SCSB的影响机理及化学反应过程,需要更多后续研究.

图9 未掺GW和掺12%GW烧结砖断面的SEM照片
Fig.9 SEM images of cross section of SCSB without and with 12% GW
(1)3种预处理的GW掺入CS中制备SCSB时,均可提高混合物料的塑限和液限.烧结后主要新产物为钾长石、斜长石、赤铁矿和莫来石等.随着GW掺量的增加,SCSB的微观孔隙数量增加,微观结构更加松散,吸水率增大,混合物料经干燥和烧结后密度降低、质量损失增大、体积收缩增大.当GW掺量为12%时,SCSB的体积收缩因为纤维骨架作用而减小,导致其抗折强度降低.
(2)PGW中的有机质含量高,可以提升CS和GW混合物料的塑性指数,烧结后不产生莫来石,微观结构最松散,微观孔隙最多;随着PGW掺量的增加,GW‑SCSB的抗压强度和抗折强度逐渐降低,当PGW掺量为12%时,GW‑SCSB的抗压强度降低48.5%,抗折强度降低66.0%.
(3)CGW的颗粒最细,能够降低混合物料的塑性指数,烧结后可以产生少量莫来石,使得SCSB的微观结构较为紧密,孔隙最少.基本上在各掺量条件下,SCSB的吸水率最低、密度最大,且抗折强度始终最大,抗压强度随着CGW掺量的提升而先增大后减小.与GW0‑SCSB相比,当CGW掺量为6%时,GW‑SCSB的抗压强度提升15.4%;当CGW掺量为12%时,GW‑SCSB的抗压强度降低6.5%,抗折强度降低34.8%.
(4)DGW的颗粒最粗,对混合物料的塑性指数影响不明显,烧结后产生相对最多的莫来石,所制备GW‑SCSB的抗压强度随着DGW掺量的增加而先增大后减小.当DGW掺量为6%时,GW‑SCSB的抗压强度提升20.0%;当DGW掺量为12%时,GW‑SCSB的抗压强度降低30.2%,抗折强度降低42.8%.
(5)当CGW掺量为6% 时,所制备的GW‑SCSB抗压强度提升,抗折强度降低不明显,效果最好.从微观角度来看,是因为CGW‑SCSB的孔隙最少,结构更加致密;从矿物组成角度来看,烧结产物中产生了莫来石,当CGW掺量较少时,烧结产物的强度提升作用占主导因素,当CGW掺量较大时,SCSB微观孔隙增多对强度的降低作用转为主导因素.
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